Yet the gen before the NES where every product was the same debunks your claim here and backs what I say about market approach, even Jim Sterling himself touched on this when he was looking at games.

You're still not making sense on the monopoly side of things because having an monopoly made GBA a massive winnner as no other platform was there to compete so it was unhampered when it sold what it did before it got dropped.

Actually you're wrong there as the west was very even when it came to portables and home consoles, GB outsold SNES, MD and NEOGEO combined in the west, GBA in the west outsold both GC and Xbox combined in the west. It was with Gen 7 where markets began to shift because of the pursuit of high end tech which changed the approach to gaming for modern gamers in the west now who now chase the experiences brought on by this approach, portables stood no chance replicating this which was a problem as that side of the market had progressed to a point where the experience on them was going to be like consoles as opposed to alternative experiences only problem is its console gaming with out the high end approach that most of the mainstream are going for in the west. The west as a resulted shifted more to consoles instead of double dipping like before, this shift also hit Japan but in the other direction as the Japanese market aren't as big a fans of the modern approach to gaming on them but found portables still heavily offered what catered to them, this is why GBA sold much less in Japan as consoles still had a footing  back then I think it was the last gen where any console did well over there as today in Japan the majority of gaming is dependent on Portables and Mobile.

GBA is not the same gen as DS and PSP that's why GBA's sales are not added to the total of the latter 2 otherwise you would have to add DS/PSP sales to 3DS and Vita sales, when you're arguing mobile boom and so on you're trying to compare an entire market to one platform to declare that the portable market has been in decline it is flawed. We have to compare both markets as a whole, mobile had a massive boom yes and portables may have shrunk from the DS/PSP era but when you bring in the GBA era and we look at the portable market as a whole compared to now it has increased over the GBA era, this shows that traditional portables as a market have not suffered at all.

3DS was competitive because of its hardware approach and handling, it's the first Nintendo portable that naturally succeeded a predecessor to actually have a competitive generational leap over its predecessor in order to properly compete this is how 3DS was reaction to what the expected Vita would be competively. This meant that developers could not only jump onboard of the platform easier from the PSP due to the large progression over the DS but the platform could be handled in a competitive manner to negate the competition. 

DS is so easily proven to be a knee jerk reaction as it wouldn't have been announced and released 3 years into the GBA's life, R&D means new platforms are always in development from all companies from release of a new one but it's obvious the are events that can trigger reactionary decisions from companies like Switch replacing both its predecessors now because one of them died 3 years in. Nintendo do things their way but believe me it does matter if the competition decide to fight you blow for blow for your market share had the PSP given Sony control of the portable market the same way they did home consoles back then with the PS1 believe me Nintendo would have been buggered as that is a tonne of revenue they would have lost out on it was a serious threat to them. They recognize the home market was lost when Sony established themselves while they were doing what they liked with the N64 and saw the same scenario possibly repeating if they left the GBA on the market instead of a more competitive one.

I don't understand how safe equates to boring. Safe just means they were financially conservative. Sony and Nintendo are where I'm doin the bulk of my current gaming so I don't see the problem here. They are the last representatives of the console realm who excel at making chart topping exclusives in house.  This should be acknowledged.

Boring because it's just like the predecessor but with more power, like a GameCube. That does not mean it is a bad console, just a boring one.

Do you mean to that it doesn't come with a gimmick as to why it's boring? Honestly I don't follow the logic because usually content decides what is boring and what isn't.

A gimmick or whatever you want to call. Dual screens, touchs screens, motion controls are new and exciting ways to play brought by interesting consoles.

Ps4 is not.

Sure, "boring" is what has made 60 millions of people to go out of their way to buy it.  And I guess the Wii U was so much fun that people thought they were just not gonna be able to handle it and decided not to buy it.  Maybe gamers around the world just considered that they were not worthy of so much fun and excitement.

But seriously, going by your logic every single console not released by Nintendo has been boring.  Maybe the whole world has a misconception of what "fun" really is.

Whatever you want believe.

Despite GBA having the market all to itself, it still got outsold by 3DS in Japan and PSP in Europe. Therefore, the argument of GBA had a monopoly = the reason why 3DS didn't outsold can't be used.

Why didn't you mention how PS1+N64+Saturn outsold the GB line? Why didn't you mention that PS2+GC+XB+Dreamcast outsold the GBA line? Or that PS3+Xb360+Wii > DS+PSP?
So you see, consoles always came out on top without hampering handheld sales.
The only real shift happened in Japan where handheld sales went up at the expense of falling consoles sales. 
If the home console market grew in the West, it clearly wasn't at the expense of handheld  sales, as GBA sales showed that it performed really well in it's short life cycle. Therefore, no shift occurred in the west.
Also, you can't deny that, on home consoles, the market went from Nintendo and Sega, to Nintendo, Sega, Sony and MS (until PS2 generation). Whereas on handhelds, it was Nintendo and Sega, then Nintendo, and Nintendo and Sony.

The only relevant difference - or the one that mattered - between 3DS and Vita was the 3D screen. But it was so relevant that 2 years into 3DS' life, they launched 2DS (no screen), because 3D wasn't that appealing anyway.
If you are talking about how easy it was or or wasn't to develop for, i seriously doubt that devs had a problem with Vita (specially when it was pretty much a portable PS3, something that devs knew pretty well).

How can you say that 3DS/Vita increased over GBA's era when GBA's lifecycle was cut short and 3DS/Vita are leaving past their supposed time (due to Sony and Nintendo not making a new portable)? You can't just ignore these important facts...
And how can you say that competition doesn't bring more customers when that's what, in your own view, made the market bigger for 3DS and Vita?

The GBA sold 65m in 4 years and Nintendo was panicking so much about the PSP that they released the DS a year before the natural time? Why? Because the ultra successful sales of GBA would fall off a cliff as soon as PSP arrived?
One can argue if DS came out to fight the PSP or to actually be a 3rd pillar, but you can't call it a weapon to fight the PSP unless you know that DS' R&D changed mid way  to make it different from PSP. 
So, despite Nintendo winning hands down in the PSP/DS generation, they still had to care about Vita? Doesn't make much sense.

Yeah, when Nintendo lost the home market to Sony it was clear that Nintendo followed Sony's footsteps as GC proved, or Wii and Wii U.
Losing market never made Nintendo copy Sony's style.

No it can because your argument hinges on one region and not the market as a whole, PSP doesn't even help your argument here as that's a competitive platform that Nintendo had to battle, it in facts backs what I'm saying that had competent competition been around GBA would have had a much harder run getting the sales it did.

PS1/Saturn/N64 came out the following gen after GB even launched, the consoles out at the time when it launch were SNES/MS/NEOGEO and it outsold them combined let alone outselling each of them. Even if we take your PS1 era attempt the GB outsold each of those consoles that gen as well despite them coming out 4-5 years after the GB's release so no Portables were always on equal footing with consoles before, PS2 was in fact the first time a console outsold the portable market platform beating out the GBA but then PS2 like the DS is an anomaly in gaming. All of this backs what I've pointed out in a shift happening in the 7th Gen.

3DS was coming off the back of the DS and was made to be more powerful than the PSP in order to help developers of key PSP flagship titles migrate over to the platform with out any compromise. Vita's high end approach pushed development costs up for portable development which turned off developers it ended up being a less powerful PS3 mini that was too expensive for most developers liking development wise and had pricing issues for the consumer while not even giving the mainstream market comparable graphical performance of the PS3 in an era where the PS4 was on the way.

Well it's easy to say the 3DS/Vita era has increased because that's the truth GBA being cut short is null and void as far as anything is concerned because it's nothing to do with anyone else if the GBA lacked competitive power to deal with any competent competition. Banging on about GBA being cut short is like going on about the original Xbox being cut short, fact is these platforms were cut short for a reason that the platform holder made the decision to do so this doesn't help your argument in anyway it's just another what if scenario that holds no ground in a debate when looking at the numbers.

Ofcourse they had to care about the Vita because PSP sold 80m anyone who follows gaming can highlight those numbers in any other gen could be market leading numbers Nintendo had to respect those numbers as those numbers indicate a competent competitor who can put up a fight. DS' numbers were also an anomaly Nintendo would be well aware the's no way to sell 160m units each gen and that if Sony built on PSP properly with Vita they would be in for a battle each gen and couldn't afford to not take the situation seriously. Like PSP/Vita or not they forced significant reactions from Nintendo, Sony unfortunately cocked up with the Vita in the end.

So, the GBA gets beaten by 3DS in Japan, in Europe by PSP, but nothing counts unless it's either entirely beaten?
That view makes no sense, to be honest. 
How can you speak of a monopoly and then ignore that despite that same monopoly it was beaten in two continents?
And that argument of being competitive or not has got nothing to do with this conversation. Gamers buy what they want, period.

Again, you ignore how long GB was on the market... 10 years! During that time, almost 2 generations went by.
GB just isn't comparable because home consoles, around NES days, were just restarting. Only natural that the NES (you can even count MS) gen sold less, but even then you have what, 70m in sales? Numbers that were achieved with less time one the market than GB had.
Then, from 1994 to 2001 you have to add the SNES and N64 generation.
If you look at how much handhelds (GB+GG) sold between 1991 and 2001, and look at how many consoles were sold in that same time frame, the difference is abysmal.
Handhelds didn't rule the market.

3DS wasn't more powerful than the PSP because of devs. What Nintendo console wasn't more powerful than the top console of the prior gen?
Dev costs also went up for those same devs who supported PSP. Did that change anything? No. Actually PSP sold a ton.
Same for Vita: did the costs went up? Surely. Was that the reason why devs (specially japanese devs) didn't support Vita? No.
As you said, price was a reason... memory cards, aswell... but the other - probably biggest - reason was that Nintendo secured the best deals (DQ, MH).
Also, it's hard to fight a 3DS at 170$ and MK7 and Mario3DLand at Christmas.

So, cutting GBA's life short when it had already sold 65m is the same as the Xbox being cut short when it had sold just 20-something millions?
Xbox had no sales potentail left. GBA, on the other hand, had a lot of sales potential. So much that, despite having two strong competitors on the market, it still managed another 16m.
If you want to ignore this "little" detail, so be it. Just don't expect me to follow suit.

So yes, having 2 distinct platforms does indeed help attract a bigger audience. And if Sony and Nintendo had replaced their respective consoles in 2015 or 2016, sales would have been even lower for 3DS+Vita.

That Nintendo respected what Sony did with the PSP, i agree. That they feared them like you imply, no.
For some reason you have this idea that if Nintendo went with old tech against a competitor like Sony, it would lose. You really give Nintendo little to no credit for what they achieved in the handheld market.
If anyone had fear, it would be Sony when they started realising that 3DS would be getting some of the most important support... exclusively.
If Nintendo feared Vita they wouldn't have made a 3DS that was just a DS+3D screen.