Can someone who is knowledgeable about smogon please give me the lowdown about what pushed Mega Lucario out of OU and into ubers?

The way I see it, while Mega Lucario is sort of strong, and hits relatively hard, he still has lots of weaknesses and isn't exactly blazing fast.

Meanwhile you have things like Mega Charizard X or Mega Metagross still stomping around in OU, and they're bulkier and faster than Mega Lucario.