"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 the losses are small. You split up the Imps and open portals with all of them. They either take the hit or deal return damage, after which the main forces finish them off. For all other races, I have more losses from clearing out neutral creatures, except perhaps for Necromancers, but even then, it's due to various reinforcements after the battle.