Homogenization is necessary if you want to have actual options. I've seen MMO's that lack it, and the result is extreme imbalances that leave certain classes restricted from most of the game's content. You basically only get to play them if you have tolerant friends.

SE has managed to strike a good balance with the tanking classes; people can literally play whatever they want in whatever content they want. Even progression groups aren't excluding anyone based on class (that's incredibly rare in an MMO).