MegaMawile as a dragon check? You do realize it's weak to both Fire and Ground, right?
So? So are other Dragon-checks in the current metagame. Look at any Steel type: Bronzong, Jirachi, Heatran, Skarmory, Forretress, Ferrothorn... All of them are famous Dragon checks because of the Steel in them. All of them are weak to either Fire, Ground, or both, yet here they stand as Dragon-stoppers. Mawile takes it a step up and is straight up immune to Dragon, can Intimidate if you predict properly and switch in on, say, Dragon Claw before it MEvolves, and resists some coverage common Dragons carry like Rock or Psychic. It's as good a Fire/Ground-weak check as any other OU Steel type.
EDIT: Minus Air Balloon Heatran, before that's brought up.
EDIT 2: Or Air Balloon Heatproof Bronzong...