That doesn't work for a mass market game. Toxicity won't be dealt with as its own problem because it would be linked directly to the talent choices a person picks. If they have X, Y, Z that are known bad choices that don't produce viable performance for that spec then they won't be invited or kicked out of any group they do get it. If you don't see how balance contributes to toxicity in the game then you don't understand much about the design of the game.
Choice just for the sake of choice isn't better. Good choices is better but we know that bad choices will exist and then we fall back in to the illusion of choice. Something you may be fine with because you get "tricked" into thinking you have a real choice. But something that won't really be a choice for the performance-gated game that WoW is.