Lol, Fairy is one of the best types in the game. Like KillerDraco said, Steel and Poison are still not very common offensive types outside of STAB users, which are easy to identify and avoid. You can pair Fairy with literally any other type and you'll probably make it better. In exchange for two uncommon weaknesses, you get a resistance to Fighting (easily one of the best offensive types out there), Dark (which is good because Dark-types got buffed in XY and Knock Off is a big deal), and Bug (not too common, but you shrug off U-turn spam like it's nothing), while also gaining an immunity to Dragon (I don't think I need to explain why this is so good). If it weren't for its new Fairy typing, Granbull would be rotting away in NU wishing that it had Miltank's reliable recovery, natural bulk, and speed as a cleric or Ursaring's power, speed, and access to Swords Dance as a Quick Feet sweeper. As is now, Granbull is a pretty good physical tank in RU and an even better one in NU, and it's all thanks to is new Fairy typing.
Also, probably the only reason Granbull is a Fairy is because its species was named "the Fairy Pokemon." Game Freak walked right into that one.