Absol's ability is good, but...

Its bulk is quite lacking, it's even frailer than Mega Absol;; If it gets hit by a scarf Garchomp's Earthquake, it's a guaranteed OHKO. Its main moves are Sucker Punch and Shadow Claw, so its offensive power is only around 30k;; It's designed to set up Swords Dance and sweep, but its bulk is like glass. If you're going to pass the Swords Dance boost, you might as well use Mega Blaziken or Charizard X.