But the way the Switch is designed is already causing issues with 3rd party support. For example, the cartridges are already impacting launch parity with other platforms. They are more expensive and are not even big enough to hold the entire game. The cartridge is only able to hold part of the game and the customer has to download the rest. For example, the physical release of NBA 2K18 was delayed because of this.That doesn't compute. You are assuming that third parties aren't pushing PS4/XB1 as much as possible (which makes no sense considering they have frame rate issues at times as well), but are pushing the Switch. As devs get more efficiency out of the x86 conoles, they will also make strides with the Switch. In fact, there's something to say that there's more efficiency to be gained with the Switch since it's the younger system that hasn't been fully taken advantage of yet. If it can run today's and last year's games, then it should theoretically be able to do so with tomorrow's games as well (of course, we don't yet know if it can play all of today's games, we only know DOOM works).
Of course, when PS5 releases, Switch won't keep up in any possible scenario.
The lack of power will undoubtedly be a blocker to the Switch's continued 3rd party support. Look at how many units the Wii sold and it still faced issues with 3rd party support. I want for Nintendo get all the third party releases just like Playstation and Xbox do, and that won't happen until Nintendo releases a console that's in the same ballpark hardware wise with the competition. I've been against mid-gen upgrade consoles, but one will be sorely needed for the Switch within the next couple of years.