Death Structures

Exactly! I have the same issue!)))
Ghosts weaken the enemy, vampires carry everyone, and dragons are physically strong, unlike Devils, who can be killed much easier than dragons.

If the mage has a general dispel spell, or there's a secondary mage with a single-target dispel, then Devils are definitely the way to go, and they can take out a hero with a single attack. In the Vortex campaign, there was much less worry about Devils because it was easy to find dispel spells and Vampire Touch in the guild, which would save the Devil after its raid behind enemy lines. But in Equilibris, everything has been cut back:( the chance of finding both is very small, and even for that, you need more than one castle with Death magic.