But no, he'll find a niche to be absurd in. He, Mega Blazekien, and Mega Lucario, even though Mega Chicken should be quickly getting the ban-hammer very quickly if he gets a physical attack boost, anyway.
The thought that Megas will deter Garchomp is absurd, though; we don't know how many there will be an in any event he's only getting one because he's popular. If anything he's one of the things other Pokemon will need Megas to deal with! Mega Mewtwo is the same, but he can take excetion just because Game Freak seems to want to brace him to deal with any future power creep. Garchomp is one of the faces of that power creep, even if Mewtwo himself can deal with him fine.
I wouldn't doubt GF giving chompy Dragon Dance as a new move for him like Dragon Pulse with Ampharos. --- Official Amnesiac Darkrai of the Pokemon X Board