While I'm also underwhelmed by Magic Bounce on a Pokemon that already has priority Taunt, what? Why would Sableye need special stats? It mainly needs defenses.Magic Bounce? There's no way Sableye's special stats can be salvaged even with a 100 point boost. What a waste of a mega evo.
I don't see any reason to use M.Sableye over M.Absol or even regular Sableye.
It could also get some points subtracted from its dump stats to add more to the defenses, ala Mega Abomasnow losing speed.