Giving Pyro a boosted jump also changes the dynamic for a bunch of old maps. In Gravelpit, does the boost mean you can then jump into the spawn-hallways for A? What about Steel's E? How does this change the Detonator since Detonator Jumping has been made redundant?
You could already make those jumps with the Detonator, at least after the buff some indeterminate time in the past. I think you can maybe even make the jump onto E's capture point on Steel with the Scorch Shot.
Pyro jetpack looks Radical and I hope there's a large degree of air control for extra fun.