Maybe Pandarens use a very guttural and animalistic language. So to an outsider it sounds like the same phrase being repeated over and over again. The problem isn't with the game. The problem is with how certain people perceive MoP to only be one thing only and never able to be anything other then childish. But part of being an adult is to know when to act childish and to know when not to.
Pandaria is hardly one big joke. If it is then all of WoW is one big joke because it exhibits no more joke worthy material then the rest of the game.