I suppose in this system, Inigo the player is only choosing to be quick. Fezzig's player is only choosing to be slow.

Of course, either can always have "adrenaline" active at all times and actually be as strong and quick as they want? So what really is the point?

Why not just have a lower strength (or Dex) then? I think there are better ways to solve whatever problem you are trying to solve.