Ice and Fire

I had the same thought. But if he suddenly decides to capture the Demon Castle out of spite, the castle is doomed, and goodbye to all subsequent reinforcements from Hell.

I agree, it's a minus. But there's no other option. A threefold advantage in the army + his magical power – I won't win the battle. Subjugation is the only option; then the size of his army will work against him.

Added after 13 hours and 14 minutes
I took down the scoundrel! I just feel bad for the Demons.

But the devils, succubi, cerberi, and horses are all safe! And half a stack of horned creatures.