WoW gradually shifted from being designed as a world to inhabit to being a content delivery system. "Content delivery system" is now the normative way of building an MMO ("theme park" design) because players bitch when there is any measurable advantage to class X under condition Y or they encountered some unfair situation. I used to bitch all the time about how warriors were fundamentally gimped if you were playing solo. Problem is that a believable world has to be able to tell players: "Yeah, that sucked. Deal with it." Because once it stops doing that it becomes obvious that the world exists for the player, not independent of the player. Long story short, you eventually reach a point where balance, convenience, and legibility can only come at the cost of the world's verisimilitude.