They are not mutually exclusive, but when you refuse to play a role because it is not minmaxed then you are not a roleplayer as, obviously, your concern is not the role but the power. Hence you are a powergamer.
Except I've never not played a role due to mechanical constraints and that is exactly WHY I like Tasha's rule.
My first DnD character was a half-orc druid. Second was a dwarf ranger with heinously poorly rolled stats. Quite frankly most of my characters are sub-optimal to the extreme because I play what I like even if it means being weaker.
But if I had Tasha's rule available I wouldn't have to make a choice between concept and effectiveness at all anymore. I'd be free to play the characters I really want to play AND still contribute to the party in a big, meaningful way.
Also this SHOULD go without saying but I'll say it anyway; the game's mechanics exist to facilitate roleplay. You can't roleplay something if the game's rules don't support that concept, which means if your concept is an orc wizard who is just as capable of wielding magic as a gnome peer you're simply out of luck. That is an impossible role to play. If you try to make that character he won't just be sub-optimal in another dimension from where the roleplay takes place. He'll be weaker within the story too, because the combat of the game are the action sequences of the story and if your stats don't reflect the level of competence you were going for it creatives a dissonance between gameplay and roleplay.
So no. Just because you want Tasha's rule does NOT mean you're only interested in powergaming or are somehow a power gamer. Real power gamers don't really care about Tasha's because they're already able to make brokenly OP characters without it. Tasha's rule just makes roleplay heavy characters closer in effectiveness than fully optimized characters.
