Basically no one enjoys doing Sastasha because they have almost none of their abilities. Lowering your damage to match the dungeon in actuality leaves you still overpowered for the dungeon, as you have plenty of options available to you that the dungeon wasn't designed for you to have. This is not a bad thing. People worked hard to get to where they are, and they should find early content easier as a result of their efforts.

Wouldn't you enjoy being able to show off your various jumps as a dragoon to a fresh new player in the level 15 dungeon? You can even make it so any non-gcd abilities receive a harsh penalty in damage if it's synced down. This means those jumps will hit for less, but it's still more damage either way.