Userbase size is only a small part of the equation although I don't think any has suggested steams active userbase is much more than Switch. Also worth noting that there is cross ownership amongst platforms. 

Nintendo 1st party software has massive attach rates as people buy the hardware primarily to play a select handful of Nintendo franchises. Nintendo could have half the userbase of Steam and still have a 1st party games competing with steams biggest releases. This goes as far back as data gives us insight to. Despite having a userbase 1/3 size of the PS1, Mario 64 (11m) sold on par with PS1s biggest titles GT & FFVII (10m)

PC/PS5 have software sales spread over a much wider portion of games. There are typically around 5x as many big software launches on Playstation/Steam versus the Switch for example. This next 4 weeks alone you're comparing MH Wilds (prequel sold 20m+), Split Fiction (prequel sold 20m+), Assasins Creed Shadows (prequel sold 20m+) to the biggest Switch release Xenoblade chronicles X remastered (last entry sold 1.8m). This is just to highlight competition on the other platforms. Even in Switches peak years, you typically have 1 or 2 major Switch releases a quarter whereas the other platforms normally have that per month. 

Ultimately both Monster Hunter and Zelda are doing crazy numbers that fans wouldn't of dreamed of a decade ago, I don't think there's much sense in a direct comparison. If we want to randomly compare high selling games, Red Dead Redemption 2 has hit 70m, when will TOTK? :D

Software sales, spending, and f2p engagement on Steam and Playstation are greater than Switch. Switch's playerbase (which is larger than Playstation's and probably not far behind Steam) is more concentrated across a smaller range of key titles and that's just a fact. I made no claim that 3rd party games don't sell on Switch.

Monster Hunter's growth is undeniably greater than Zelda's all things considered. Your sales average metric is misleading and leaves out important details. MH World was expected to sell 1.5-3 million lifetime, because the last and most successful home console MH game prior to World sold poorly outside Japan (Tri). World will sell over 30 million, the vast majority of which outside Japan. Every first mainline Zelda game sold quite well. Particularly Zelda 1 with 6.5 million, Ocarina of Time with 7.5+ million (on a tiny install base at that), Twilight Princess with 9 million, and BotW with 35+ million. 2nd Zelda games within a generation always sold worse than the first and that theme is going to continue with TotK unless they "DX" it. Wilds should beat it, especially if ported to Switch 2.

Beyond sales, Zelda always had a special significance as one of the most influential and greatest game franchises of all time. Monster Hunter, even the portable line, was niche outside Japan.

The first ever Zelda game sold over 6.5 million (which is massive for its time). The first Monster Hunter game sold less a million including Japan, the odd region where Monster Hunter quickly became huge. The more angles you consider, the more obvious it is that Monster Hunter's growth is on a completely different level. Zelda's growth is more in line with God of War and Spider-Man's.

The argument about competition's core foundation is to push the inference of sales and output from third parties which is simply no longer the case with Switch, the flaw in this argument is that while PC and PS5 have more competition it is simply not as great a gap to the point that it makes first party titles perform the way they do.

I've played MH since the original PS2 release believe me your argument is the one that is misleading, the last console MH game was on a single platform for a start and required the platform holder Nintendo to do all the marketing and publishing themselves outside Japan it wasn't going to release in the west otherwise and to top it off it was only the second console game to come to the west after the original PS2 game. ALTTP, WW, PH, ALBW, LA(OG), Oracles all averaged in at 4m or less and were the first Zelda games on their platform that's five compared to the three exceptions, fact is LOZ, OOT and TP sold what they did because the were factors not tied to the games at play this is why the series didn't stay at those numbers and the rest of the games average 4m for example the first Zelda game which you used in your argument was one of the earliest games in a new era of gaming after the crash, in comparison the first Monster Hunter game had flawed execution as a game with wayward controls with lack of content literally eight or so monsters offline and the rest requiring online to access coupled with the dreadful handling of PS2 online especially outside of Japan doomed it. TOTK will be selling until the next mainline Zelda game much like BOTW (it's been selling steadily for eight years now and still hitting 1m a quarter at 33m) has so in the four or five years until then it'll be selling with the new brand power this is why I doubt Wild will outsell it in the end even if Wild is ported to Switch 2 I can see maybe only a few extra mil at most much like the ports of Rise after NS/PC.

The are many great and influential franchises that doesn't translate into mainstream sales though Metroid is an example of this so it hasn't got as much bearing rating a series growth especially as prestige is something the masses aren't as aware of, your stance is pivoting to the niche argument with MH outside Japan well here is the irony Zelda has been niche in Japan for a while before BOTW even TP the highest selling only shifted 600k over the, Japan is one of the three major regions and games like the Freedom/Portable were at times outselling Zelda titles totals in Japan alone Freedom 3 sol 4.9m in Japan alone had it had a western release even with niche sales it would stand at a total comparable to the top three selling Zelda titles so it effectively balances out.

The growth of both titles is as equally impressive as each other same thing with GOW, Spiderman etc.

Can you please list for me every game on the Nintendo Switch from a third party developer that has sold 5m+ units? I’m curious to see how big it is. I’m fairly sure that the Switch is still massively far behind in its ability to sell third party titles to a mass audience. 

The one big example I can think of is Monster Hunter: Rise and that’s a game with a very big Japanese audience, and a history on handhelds(both hugely in the Switch’s favour) and that game did very well but it’s sales were heavily skewed towards Japan. Outside of Japan it likely sold around 20-25% of what World did.

Where did you get the 5m number from dude? As for Rise Capcom confirmed Rise's sales were 50/50 on Switch between the west and Japan this means at least 4m sales are in the west going by the last sales update for Switch before the PC version arrived, selling to mass audiences isn't the problem it's when you're getting the games well after the original releases for full price on other platforms that is as that requires careful handling.

5m is an arbitrarily chosen number. How about 4m? I can probably list like 100 games that sold 4m+ copies on the PS4/PS5 or PC. How many on the Switch? If the competition on the Switch is just as high then there would also be large numbers of third party games selling these kind of numbers.

Instead the only games selling big numbers are all by the same company that can release their games in the order they desire to minimise cannibalisation and competition among products. That’s a captive market for Nintendo.

While I agree with your take on the comparison, I think that you are placing the segmented audience of pre-World MH it too much of a focus here when talking about the IP in general. The people who, at least initially, bought World were most likely a largely different audience than the Japanese and handheld-centric most popular MH games up to that point but latter audience needs to accounted anyways since we are talking about IP growth.

PSP titles ended up with quite high numbers, especially for their time, by the last entries with almost 4m million in the case of Unite and almost 5 million for MHP3rd.

Same for the 3DS titles, with 4U and Gen reaching 4.2 and 4.3 respectively. Now, as I said before, World's audience is mostly different people, even by definition, as IIRC, Tri's 1million western sales were the most the series had sold up until then in the west with probably only 4U topping it (or GU). But those sales should be counted into the IPs status at the time.

Still, Worlds sales were explosive, especially taking into account that the cultural relevance of Zelda has been much greater throughout generations and its previous peaks also much higher.

Are you kidding or something? Nintendo has their console open to every major third party publisher, they can publish everything they make on Switch if they so choose. But in reality the only major company that puts major effort into Nintendo consoles are Nintendo themselves, which means that they are the only one that will find major success on their consoles.

How is the Switch a captive market? Consumers have chosen to buy the Switch, even though they know they won't be able to play Call of Duty or other major franchises on the console, meaning Nintendo games themselves are so attractive that people choose to buy the Switch even though it gets no major third party support.

Can you list major day and date third party games on Switch that should sell 4-5 million copies on Switch but fail to do so? I can only see minor third party games that don't sell a lot on any console coming day and date on Switch. But some indie games have had major success on Switch, Stardew Valley for example has sold 7,9 million copies on Switch:

Stardew Valley continues its wholesome farming dominance with latest sales milestone | Eurogamer.net

You won't see any difference on the Switch 2, third parties will never commit to releasing big games day and date on any Nintendo console, so it will once again be up to Nintendo themselves to increase the appeal of the Switch 2.

How competitive a market is determined by reality, not what is possible. It’s possible that any company can sell Cola but it still means that Coca Cola is the dominant market force.

Gamers don’t particularly buy third party numbers in big numbers on Switch, and companies don’t make any particular effort to make their games available on the Switch. That’s the reality. It’s not about what is possible, or under even conditions. The reality is 90% of all the big selling games are made by the one company. That’s not real competition. 

The is a flipside to that argument though as the possibility is still a factor hence you say Coca Cola I'll say it's more iPhone where it has a strong position but not one that is unmovable once someone puts in the work as seen with Samsung and Huawei.

This is why Rise sold well because it was handled the same way they handled World, Generations on Switch didn't perform like Rise and that's because it wasn't handled in the same way highlighting the possibility is a factor under even conditions, for example Rise on Xbox and PS4 has performed below par and that's because it was handled on those the platforms the same way most third parties approach their games on Switch so he or she (sorry don't know) has a point.