Pokémon Let´s Go will probably be my first Pkmn game ever since B/W and I am really looking forward to play it. I do understand the backlash from core fans and, honestly, I am a bit bothered by some it. Some of the things announced ARE shitty, like Mew behind a paywall and the lack of motionless options for capture (It doesn't bother me at all, but some people will be). Fortunately, this is not the DS era anymore, the games now will be actually patchable, so vocal and reasonable backlash can be make it's way into the game. However, I will say there is some conclusion jumping from detractors:
Are we sure that Mew will it only be available this way? Are we really sure there won't be other ways to get it without having to expend money? If it really there isn't, then GF deserves all backlash possible until the revert this.
Also, are we really sure that we won't see any other gen Pokémon eventually? I find unlikely that Let'Go won't interact, at some extend, with the gen 8 games at all. So I think the 656 Pkmn data will be in the game and may become available later events or maybe even postgame content, notthat different from how FireRed/Leaf Green allowed Gen 2 and Gen 3.