Killers CAN be overpowered...
Here me out no bait:
If a killer decides to use all the strongest things, he can, in fact, become more powerful than the survivors.
Now, do killers want to play like this? Most want to play killer with chases in mind. The problem is that if a killer plays fair (follows the way the game wants the killer to play), then it is set up for a 1v1.
So in the end, yes: killers can in fact be more powerful. But most dont like that, as it feels not fun to get only brutal killer after getting a 4k.
Tl;dr killers are overpowered when you put on the strongest things.