THIS IS OPTIONAL, BEFORE YOU GO RAGE ABOUT ENGINEERS, READ THIS ENTIRE POST
How about a trait that changes your turrets to moving “siege engines”? Each race would have a different style of moving turret, and the skills would have three tiers.
Tier 1: Regular moving turrets
Tier 2: Obedient turrets
Tier 3: Healing/Reviving turrets
Now, this is only a suggestion, there are still kinks to work out. I’m open to suggestions, as long as they are constructive.