While devolving might make it easier on aliens, I'm completly against it.
First, It would make the tyrant the ultimate alien, since it could do everything and anything, go adv goon, snipe stuff, charge as a tyrant, then hide as a dretch. See the issue?
First, tyrants are simply brute force. If it had the ability to be anything else, the game would be too alien biased.
Second, if you're stuck somewhere as a tyrant, have a dretch lift you. I've lifted and been lifted numerous times. The beauty about tyrant, goon and granger lifts is teamplay.
Third, logic!
While humans have the ability to hold diferent tools and weapons, evolution is biological thus logicaly ireversable. Think of a butterfly. A butterfly can't go back into a cocoon and devolve into a larva, etc.
Aliens follow a similar rule.
All we need to even things out is have aliens have the ability to evolve around the OM, regardles of human presence. Otherwise, the game is fine as it is, IMO.