Mature MMORPGs. What does that phrase conjure up for you? Probably the same sorts of things that the word 'mature' inspires in everybody, when linked with video games: boobs and violence. Oh, and hints of rape.
You can keep your dark story in which millions are slaughtered. You can keep your exposed cleavage and knee length bosom. You can even keep your gratuitous violence. These aren't the sorts of things that give credence a certain game being mature or not. They're adult, but they're not mature.