In reality, despite a good start, attacking with demons inevitably leads to significant losses. They are generally poor at capturing castles. This isn't like the Necropolis, where capturing a castle allows them to double in size. Ereb, you're wrong about the Demons – with luck, they can crush anyone, even armored units, let alone those dogs with succubi. I would say they form the backbone of the army. Horses are also not bad in attack, but they are destroyed quickly. The Imps that you praise are a bit slow. However, a level 7 demon hero is very effective at crushing enemies, although the army is dwindling rapidly at that time.