In principle, everything is correct, but I destroyed the ballista and Deleb with the help of summoned dragons (the hero had a perk that increases the army's speed when storming castles, so the dragons easily reached their destination), and I was able to restore the harpies either with vampirism or some other way, I don't remember). The losses were insignificant.
Regarding the Devil, you could have tried replaying. I noticed that the course of the battle depends on many factors, even on who and where you place them. After gaining control over the imps (which is ideal for the beginning of the battle), you could try casting berserk + mass slow + vampirism on key units. It seems that resistance won't affect them.
It doesn't work). It's just that his army almost one-shots all of my units. As soon as my harpies and scouts are defeated, I immediately feel sad). Here, the only chance is to control the imps and defeat everyone with his own troops. I'm telling you, I prolonged the game by having an army of... 500 imps, 10,000 lesser imps, 2,000 succubi, etc. Here, only a mistake in the course of the game can be corrected by dark magic and the "Shaar" spell
