Historically speaking, less 3rd party support equates to less sales for Nintendo consoles. Look at N64, GC, and WiiU for proof. Each one had less support than the last, and each had less sales than the last. The only exception to that rule is the Wii.
It would seem that some people do not understand that while 1st party games are the main reason people choose Nintendo, and even get away with less support than the competition, having 3rd party support to some extent is still important for the success of the device.
You need to examine the date properly, and that means that you have to include all Nintendo consoles. Then you'll realize that the Wii isn't the only exception.
Nowadays the AAA third party support is heavily dominated by American and European publishers. Successful Nintendo consoles without the support of those publishers: NES, GB/C, SNES, GBA, DS, Wii, 3DS, Switch. Unsuccessful Nintendo consoles: N64, GC, Wii U. Given that it's 8 vs. 3, you should question the premise you have.
Furthermore, since its launch the Switch has received only a single digit percentage of the AAA third party games released since March 2017. Switch has sold very well regardless. The fear/hope that Switch will be in trouble once that single digit percentage drops to a smaller single digit percentage is irrational.
You see the problem here is that you are cherry picking what facts you want to use for this topic.
Acting like the NES and SNES did not need western 3rd party because most 3rd party devs were from Japan does not exactly qualify as a quality argument. The fact is, the NES and SNES had the majority of 3rd party support as a whole, which is the real factor.
Also we are not talking about the handheld market, so to throw those in there just to pad the numbers is also not a good way to look at things. All that does is enable people who try to say, "Switch is only a handheld that connects to the TV, and therefore sales should not be compared to PS or XB." The fact is that the Switch is a hybrid home console with portable functionality, as that is what it is advertised and sold as. Furthermore their handhelds have had adequate 3rd party support as a whole, cherry picking western devs is just a way to make it look like they had less than what they did.
So unless you are ready to jump on the bandwagon of either "Nintendo dropped out of consoles" or "with the Switch Lite making the Switch a portable only device, a next gen home console from Nintendo is right around the corner", I suggest you re-evaluate your the data you are briging to the table.