Leader abilities when not in the leader position.

It might be too complex, I'll give you that. It was just a thought I had today when I cringe looking at Vader's lead zeta'd and I don't use it anymore. Maybe make it part of the zeta portion of the ability? That way you're still picking and choosing what to upgrade, but if you spent the resources on it with a zeta it is still usable even when the leader portion is not anymore due to the evolving game.