queen isn't overpowered because every player is both a queen and pawn
it's like calling the bottle UP
it's not like in CS where there is a risk of running a certain class if one class is objectively better than all others either since you can keep running that class indefinately even if you're being out DMd and losing every round
getting carried is a function of skill difference, not class, and even then demo scales the most with a high skill differential since he has 12 rockets and his only downside is they're hard to aim if the skill level is even
if you want to make the game balanced for HL/Pubs, without ruining 6s, you'd need to make it so there's no free wins (there aren't any in 6s) by nerfing defensive heavy and engi stacks, and nerfing the ability of individual demomen to win with basically no contest from lower skill players because demo is so powerful if he hits shots