If your server is pretty new. I wouldn't be surprised. Even pre 2.0, early to mid servers are flooded with MB, so with post 2.0, there's just more of them.

But if you're talking a more mature servers with plentiful of level 85 capped players, this isn't actually the case, there's is still a large mix of players in various classes.

There is no 1 class that kills everyone in mature servers. Every class got its own advantages, and at the same power level in later stages, its all down to tactics, refines, runes, etc. Since all talents are open and every class has its advantages with their own respective ninjas that can compliment each class separately.