fwiw i think even with that aspect, it's not blending the lines that much.No, it's a different issue.
Due to the nature of the encounters in those games (on overworld, you can pick what to use, on top of candies in Let's go and raids in SwSh) it's much more difficult to make a "tierlist" due to the fact honestly everything is usable.
We had some chat about SwSh tierlist, and the biggest barrier to make one is the fact the Wild Area offers an *absurd* amount of pokemon right away, and that's not even factoring time manipulation or raid usage.
Part of the "tiering" system was due to the rarity and position of the pokemon (es, if a pokemon stomps the game but it's a 1% spawn in a backtrack area, say Salamence in USUM), it'd be low tier due to the time investment required. This is nearly nonexistant in SwSh, partly due to overworld encounters (allowing you to see the spawns so not requiring to waste time running in grass), and partly due to the insane amount of available pokemon early in the game, even in the first half of the wild area itself.
While you get to see all the spawns at once, they stick around for a while so you either have ot routinely burn through the encounters, wait for them to despawn or constantly reload the area. It was easier for me to find that 2% Drakloak encounter at lake of outrage, but ti still took a fair amount of shuffling them in & out of the spawn radius.
There's also the encounters that don't spawn on the overworld, like the 2% encounters from hell that litter the routes & wild area that only spawn in shaking grass. But routes still have their own set of pokemon that show up there specifically in general.
-Weather, though we've talked about that in the other thread. There's overlap between pokemon, areas and weathers and some weathers are purposely later in the game (or post game!) and probably rarer in general, especially if we dont account for day manipulation. That'll definitely affect rankings.
-Here's a quirky one: size of the pokemon. Smaller pokemon especially blend in with the grass. One time I ran into a salandit and didn't even realize it and wasn't able to find another one because it blended in. Mimikyu is tiny and only shows on the overworld in one specific patch of grass in the fog.
And this is all just focusing on availability and not the other factors in tiering like how useful it is, movepool considerations, direct competition, dead periods, etc