Inferno tactics.

...
I can't recall the author of this argument right now, but I agree with his words.

I'll join in. Demonology has potential, but it's not entirely clear.
If there are external sources for creating level 1 units, then they can be converted into demons.
But buying back troops and then converting them is tedious and not obvious.

I still haven't been able to understand the creator's intention - why is such demonology needed? :)