Well, I "completed" this map. Or, rather, I followed the original storyline.
The thing was, I wasn't building up an army. I was constantly "on the run," exploring the Dungeon, and at the same time, farming Nibros. I only leveled up Baron because I thought he was a core hero, and his "accidental" death would ruin my entire Walkthrough. As a result, it didn't turn out as cool as it would have with a ranged master or a local Axel. However, my Baron turned out to be very strong: a full set of Gnome King's armor, almost all stats at 30-25, level 30. So, I kill the demon, go to talk to Bernabar, a messenger runs up to me, and... the beginning of the end arrives.
The Barbarian heroes, although they looked intimidating with their giant armies, crumbled against Baron like bandits under the blows of Murasame. I took two cities and started looking for a third. I went the wrong way and got two rather impressive Barbarians in my rear. While Baron was leading a campaign to suppress the slaves, his right-hand man, Bernabar, gathered an army from two cities and buildings. As a result, the strongest Barbarian stack was successfully destroyed by Baron, and Axel started chasing the second, slightly smaller one. While he was chasing, Baron managed to take the third city and find an impassable Orcish garrison (by the way, with my rather modest army, a "high" difficulty level was shown there, and that was with a cloud of Cyclops). And by the time the siege was successfully completed, the last Orcish army was defeated.
I was just about to rejoice in the victory when he came from the other end of the map... That damn Kurak!
He made it to the Raven's Nest and burned it to the ground. And do you know why? Because my entire army was already destroyed before him, in numerous battles with demons and garrisons.
Well, damn it, who knew that I needed to sit and build up soldiers? I thought that since enough weeks had passed, one Baron and a border garrison would be enough.