As promised, I played as soon as I had time. I chose a veteran, and with great difficulty, I cleared the territory without any losses and moved on to the dwarves after a month and three weeks. There, two heroes with armies 15 times larger than mine appeared. No, I would have had a chance if I had leveled up a dark mage, as there were spells like Mass Teleportation + Book of Teleportation everywhere, but as it is, there's no way. In addition, one of the dwarves turned out to be an expert in darkness. But overall, it was very interesting; I just don't understand why there's fog all around and why the AI moves so incredibly slowly.
I'll try a lower difficulty later.