Some healers were good for single target healing and shit for multiple targets, other healers were the oposite. Now all healers are "equally" good on both. Same goes for the dps classes. We have all received new abilities with the new expansions that gave us "that thing that other class had and i didnt".
For example (i will generalize, im sure there will be exceptions), all classes have a stun now, all classes have a snare remover now, all classes have an aoe healing ability now, all classes have a speed bust ability now... etc.
So, wanting to fit back in a distinguising mechanic into a game that doesnt work like that anymore... would make things... "chaotic"?