I would not agree. MoP is actually WOTLK + Cata/Mop leveling, which brings up more content IMO. Mechanics are bad? Wouldn't say so. Talents are much more fun to choose, and they actually contribute to the combat itself. More maps, more hp making it more forgiving for the mistakes you make in PVP, better endgame with more raids (wotlk has lich king raid and that's very respectable, but nothing beside that one)... endless list if you ask me. i think it's more about the nostalgia because the most of the players played WoW hardcore during WOTLK, and that horrible Cataclysm expansion actually made MOP look bad, even tho it's not.
Cata is bad, not MoP.