This makes absolutely no sense. It's one thing to make certain characters slightly more suited for PVM and others for PVP(let's say, about 30% more suited), but the gap shouldn't be nearly as massive as that, otherwise you are basically telling everyone who likes to play a certain character that they have to choose certain portions of the game that are playable(for them), and just ignore everything else. This is made even worse by the fact that unless they change class, they are stuck with that character until the next DB.
I get that a lot of the unbalance is present in Mu at its core(and therefore not the server's fault, or yours/ADMIN's), but saying it's "fine" that three BK's get out-DPS'ed by a single character because BK is better at PVP is just laughable. The goal should be to make the characters strength in all areas as close as possible, which is what all successful MMO's do.