Well, it depends on the game system how well this pans out - in FATE Core for instance you would have no problems letting both Thor and the potted plant contribute to the narrative since either of you can invoke aspects just fine. I won't say you can't have fun in a game like that, but I would claim that D&D is ill-suited to make the potted plant interesting to play.
Either way, I do agree that powergaming is a player thing, not a character thing - there are situations in which a powergamer sets out to be unbeatable and stronger than everyone else, and then at the table just isn't - which doesn't make the player less insufferable. But on the other hand, there's players who overshadow the rest of the party without meaning to.