I think AI bots don’t know Deathwing is Unstoppable.
I saw AI Qhira and AI Xul repeatedly casting their E spells (swing or root) on Deathwing, which has basically zero effect. The tiny damage done isn’t worth putting the ability on cooldown.
I think your bots may have little more issues than just knowing what ability to use on which hero. However, E can still spawn skeletons or inflict bonus damage debuff based on talent choice.