[quote=Jerkchicken]
Because better skills and moves are better than just some one use move that'll be popping up irregularly
[/quote]

The use of a mystic arte won't necessarily create any draw backs from any style or Etras. It won't be irregular, but there will be a use-limit, like once every 'dungeon' type thing. And it'll be more of a storyline element more than anything.