I have dk, monk and dh as rerolls now but I never created them during the xpac they came with so IMO an expension being crap has nothing to do with a new class being introduced with it or not.
And it doesn't matter if you "don't care about the balance of the game, or how pvp gets more f***ed because of adding a new class and that there are so many classes already in the game blabla".... because those are valid arguments against new classes even if you don't care.