Yes we would be doing all stories for sure. Anything post-credits wouldn't count imo, similar to how the other lists have done things.I have a feel that sadly SV has the same issue of SwSh where having access to (almost) the entire Pokedex right from the start makes creating a tier list somewhat of a issue...
HOWEVER...
one thing that could reliably be used as base for a tier list would be trying to rank mons based on their ability to be used for the entirety of the game. Ultimately we're looking at 8 gyms, 5 team star boss fights, and the 5 titan fights, as well as e4 and the other battles before the final arc.
I definitely remind some pokemon being significantly nonimpressive back when I played to the point of regretting having even bothered to level them, so if a tierlist attempt had to be made, it would probably have to consider "all stories" as metric, rather than availability (as with very few exception, pretty much every pokemon in the game can be obtained as soon as you are out of the tutorial, or in worst case after having beaten enough gyms to have lvl 30 obedience, high level fixed tera encounters nonwhitstanding)
How do you feel about potentially enforcing a set order for the gyms based on the level curve? I'm 50/50 on it, it provides a clearer path but you could probably roundhouse the harder bosses when you know what to expect.
In terms of bad mons, I have heard horror stories about Tarontula lol, and I wasn't a fan of Shroodle