While I do agree that this game is not ambitious enough with regards to what it does with the Switch's hardware. I think a comparison between a game that has a cartoony art with a level of cel shading style (particularly in the environment) to one that is trying to look realistic is not really valid. Even games like Mario Odyssey and Breath of the Wild, both of which have a cartoony art style (BotW is also cel shaded), do not have that level of texturing and detail presented above. When I look at the ideal art and corresponding level of detail for a Pokemon game I don't personally think of realistic games (because that is out of character for the anime style that Pokemon is going for) but rather I think of games such as the Ni No Kuni series on PS3/PS4 (and the Let's Go series falls short of those games; but that is where I would ideally like the core RPG for 2019 to be at).

Confirmed that the 2019 games will not be influenced by Pokemon Go.

Okay, but even if we compare it to a cartoony 360 game like, say, Sonic Generations, we're still seeing better textures and detail on the much weaker hardware:

But the 2020 games will!!!

I'm selfishly praying Let's Go fails miserably so it doesn't become another series that drains resources from stuff I'll actually play.

Drain resources from where exactly?  All the company does is release Pokemon games.  The core series isn't likely to shift from its new game every 3-4 years schedule with a remake and repackaging job tossed in between.  Everything else is basically a bunch of oddball hit and miss side projects, and I don't really expect that they'll be altered all that much by a gusher of cash that'll come if Let's Go becomes a hit.  If anything, it'll encourage more oddball side projects.

As I said, I don't think the overlap of people who care and people who complain is particularly significant.

You're also more generous than me.  People who are disappointed don't seem to understand the basic concept of artistic choices when it comes to video games.  The style here is obviously meant to be laid-back and inviting.

I can only imagine what the same people say when a game really goes old school and employs pixel art.

Again art style is still not one to one, but Sonic Generations and Unleashed are more appropriate for comparing compared to the more realistic game.

It is completely an issue of art style.  You're just pointing out a similar but distinct art style of Sonic and wondering why they don't do that instead.  I'm pointing out that they made the conscious decision to stick with the style shown.