Ohh this, is.... Wow.

... you know Sony and Microsoft are releasing new console that are going to making porting to the Switch even more difficult than in it is now, right? Even now Switch ports are mostly all limited to games that aren't very resource intensive. Why on earth would this actually get better?

To start, I definitely do not agree with him about it becoming the best selling console ever but I agree with him about support growing.

I highly doubt that AAA support will grow much but then again he never mentioned anything about AAA support. I think in 2019/2020 we will see support grow quite a bit A-AA titles.

Things like indies, Japanese games, kid/family titles, previous gen ports/remasters, retro compilations, free to play games, and various current gen down ports will all see improved support on Switch.

zorg1000 already gave an excellent answer to this.  But I would like to add that Switch by far the best selling platform in Japan right now.  That means it is the default platform for 95% of Japanese games currently in development.  These developers are not even questioning if their game should come to Switch.  Instead they are asking, "is it even worth it to port to a Sony/Microsoft platform?"  In very many cases that answer will be "no". 

Switch is going to have a ton of third party exclusives when all is said and done.  Sure most of these exclusives will be indie or Japanese, but they will still be third party exclusives.

Japanese developers care for more than just Japan though. For bigger games and western focused games, the Playstation brand will likely still be their go to choice and since it's so easy to port to Xbox, it will likely get a large percentage of those games as well and Switch will get the ones that can feasibly be ported to it.

Where Switch will truly shine is in the medium sized titles. Many of these games were cross-gen between Vita/PS3/PS4 up until a year or so ago, 8n a couple years that will transition to NSW/PS4/PS5.

Also many of studios who made 3DS exclusives will likely transition to Switch.

We are basically saying the same thing.  The 5% of Japanese games that don't come to Switch will be higher budget games.  If the next new Final Fantasy or Resident Evil doesn't come to Switch then it won't surprise me much.  Most Japanese games have a small-medium budget though.  It is mostly Western developers that are known for cutting edge graphics and huge budgets.

Also all the developers that were making games for 3DS and Vita or cross-gen Vita/PS3/PS4, all of these games will come to Switch (as you said).  Any game which sells 4m+ in Japan will come to Switch like Dragon Quest or the next Monster Hunter.  Lots and lots of Japanese games are coming to Switch.

Who gives a shit about third party anymore?

The switch pretty much proved itself to be widely successful with just Nintendo first party support.

The ps5 or Xbox720 or whatever games will have zero effects on Switch.

Just like how Red Dead, Spider-Man, God of War right now having no effects on current switch sales.

Two years later, that big red "10-20M" is staring back at me. Knowing. Judging. Mocking.

Wait, why are you putting so much emphasis on Japan? As well as the Switch is selling there, it still represents less than 25% of Switch sales. Still A Nintendo/handheld console getting "95%" of Japanese games is the status quo.  It was the same for the DS, the same for the Vita, the same for the PSP, and so on. It would be surprising if the Switch didn't get the vast majority of Japanese games on its platform. Why should anyone care when considering overall sales? What difference does that make? What percentage of those Japanese games are released outside of Japan? How many of them sell more than 500K copies outside of Japan? Look how many Japanese games were released on the Vita in 2018 if you need to put in perspective how little that matters for overall platform sales. For example, why should  a prospective buyer care at all if the next game from the makers of "Tokyo Xanadu" or the hundreds of other developers like them doesn't come to a Playstation or Xbox next time around? How many people is that actually going to sway into buying a Switch? If the answer to that isn't "tens of millions of people" then it really doesn't matter.

At the end of the day, It doesn't matter how many third party exclusives the Switch has, it matters how many third party exclusives that pushes a prospective buyer into buying one. Indies and Japanese games don't exactly have a great track record of leading to world-wide sales. If they did, the Vita would have been FAR more successful than it was. At the end of the day, the Switch is going to get less and less third party system sellers after Sony and MS release new consoles, and that's all that really matters.

Your argument kind of hits a wall because you're going about third party titles that sell the platform when no Nintendo platform really relies on third party to sell itself and what's ironic is the third parties that do have some semblance of an impact are often the Japanese games as they tend to be the only games that mirror the appeal of what the first party games have which actually backs his point on eastern developers being significant.

Out of all the Switch games only one third party game has actually had an impact on sales and that was Octopath all the other system sellers have been first party titles and they've had no problem selling the platform even when games like RDR2, GOW, Spiderman etc... have come out the NS even in total  sales outsold the PS4 in NA for 2018 according to NPD highlighting the reality of the situation is what you're trying to say is a factor really has no bearing on the Switch.