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.
If your argument is that third party titles don't really matter in the grand scheme of things for Nintendo platforms then why are we talking about it? Also, isn't it ironic that you claim that Japanese games that have an impact are ones that mirrors the appeal of first party games, and then mention Octopath Traveller, which isn't like any major first party Nintendo game that Nintendo has made in years. You're contradicting yourself.
Great, the Switch outsold a console in the 5th year of its life that experienced declining sales in the US. So what? That was pretty much expected universally. I'd be concerned if it didn't.