Switch is sold as hybrid, perceived as such and getting games as if it is a portable. If you haven't paid attention, Switch is inheriting all the support the 3DS and Vita got without a problem. You answered your own question wrong. But most importantly, Switch is already tracking ahead of the 3DS and will grow the gap significantly in the next few months.

Are you insinuating that PS4 and XB1 aren't real competition? They are cheaper than Switch and have bigger game libraries to fall back on. Do you really believe that more expensive consoles with smaller game libraries will make Switch unattractive all of a sudden?

Your whole line of thinking is very similar to the concerns that were raised during the Wii era. Nintendo ended up listening and made the Wii U, and the market sent a crystal clear message that AAA third party games aren't a selling point for a Nintendo console. None of those third party games managed to sell more than one million copies. Wii U wasn't the only console where Nintendo placed importance on AAA third party content though; there was also the GameCube. A decade before the Wii U Nintendo had already received the same message from the market. Nintendo's worst selling consoles are the ones that pursued the games you argue they should pursue.

Do you have any sales data that supports any of the points you are making?

It's selling well even during slow seasons, it's second only to PS4, even managing to beat it a few weeks in a row, 3rd party support is good and growing and SW sales are in line with home consoles, so with the hybryd Ninty should enjoy a HW success that, Wii apart, it usually gets with portables, but eventually reaching an attach rate at home console levels. If this isn't a success, I don't know what else could be. Probably PS4 lifetime sales will be higher, but NS should anyway enter the Top 10 ever. Last, but not least, once again Ninty showed the way to go, this time for console makers that otherwise could succeed only in home or portable market, but can't, or can't anymore in both, and this getting, and making 3rd party devs get, a higher return on investments.

Lol acting like Luigi's Mansion and FE don't have results from the home console market.

Either way, the series I mentioned all were most popular on handhelds. What does it take to be considered mainly handheld title?

Your problem is that you constantly draw false conclusions to support your stance.

Sure, Switch didnt cause PS4/XBO sales to drop but who cares? I could turn it around and say PS4 in 2017 wasnt a primary console because despite having it's best year it couldn't stop Switch from having one of the best launch years in history. That statement would be equally silly because it draws a false conclusion with nothing to back it up.

The people who buy a $400+ console at launch are typically not the same people who buy a sub-$200 device that's ~4 years old.

I know $400 wont be an issue for PS5, it will sell great at that price, that however does not mean Switch cannot also do very well at $199 around the same time.

Just like Genesis did not stop NES from selling in 1989/1990 or Saturn/PS1 stop SNES in 1995/1996 or PS2 stop PS1 in 2000/2001 or PS3/360/Wii stop PS2 in 2006/2007 or PS4/XBO stop 3DS in 2014/2015, or Switch stop PS4/XBO in 2017/2018, PS5/XB4 will not stop Switch in 2020/2021.

I don't deny that diversifying their lineup would be nice, but I'm really not seeing the next PS/Xbox as being a significant threat to Switch, for the same reason lions aren't driving vultures or hyenas to extinction, they occupy different ecological niches.

People buy PS/Xbox to play AAA third party blockbusters, but they buy Switch primarily for the flexibility/convenience of it's "play at home and on the go" premise and for the first party exclusives. That's why, as you say, PS4/Xbone sales were not affected much by Switch's arrival, because they're not in direct competition. PS5/Nextbox will similarly not be in direct competition, because those systems will take over the same niche PS4/Xbone currently fill.

Who cares?
So, not causing sales to go down and causing sales to go down mean the same thing to you?

You can turn things around. You'll be ignoring pretty much everything, but ok.

"The people who buy a $400+ console at launch are typically not the same people who buy a sub-$200 device that's ~4 years old."
It's true.
But at the same time, that situation in not the same when you have a console that is dominant or a console that's living off the dominant's market.
If the shift from PS4 to PS5 is as fast as it was from PS3 to PS4, then things might not go as one would expect, specially in the case of where a console like Switch is still to exposed to that "shifting" market.

I'm not saying with this that sales will fall of a cliff or that the blow will be really hard, but it might be the case where Switch's life cycle is substantially reduced. And when you are dependant on one console (no signs of that changing) then… things might not go so swiftly for Nintendo.

In other words, if we saw - or start seeing - Switch really building it's own market (stealing customers), i would be less concerned.

FE and LM were more popular on handhelds, so far.
There hasn't been a home console LM since the 3DS game and the same goes for FE.
We need to wait for the results to see how they fair on Switch. 

It would be more than nice! If Nintendo wants to really put their foot on that market for good they can't rely on just 1st party games or paid exclusives of that kind - even if for the sole reason that Sony and MS would easily outbid them. That's why change needs to come from within.

I do agree that Switch is different enough to make itself a more than appealing product to Sony and MS users, but we shouldn't overlook how this success came to be.
Do you really believe if there weren't 80+ million PS4 and XB1s sold when Switch came out, that it would have had this level of success?

If the data we have show that, despite 15+ million Switches out there (2017), PS4 and XB1 could still act as if it was nothing, then it's safe to assume that if they aren't choosing Switch over PS4 or XB1 now, despite all the bells and whistles, then the same would happen if they were released around the same time or, that when PS5 and XB2 arrive, there's a real risk of that market simplying opting for the new consoles.

It's really a question of priorities.