"Weak demons"??

People are writing nonsense here; it's actually very effective for Demons to clear out neutral creatures. Perhaps it might be a bit challenging at the very beginning, but even then, the losses are small. You split up your Imps and open portals with all of them. They either absorb the initial attack or deal retaliatory damage, after which the main forces finish them off. I have more losses from clearing neutral creatures with all other factions, except perhaps Necromancers, and even then, it's due to various reinforcements after the battle.