In the end, I wasted an extra week running around to collect luck-boosting items. With a luck stat of 4, I barely managed to win with minimal losses.
P.S. I reached the boss of the first mission. What a "recruit"!
I only won thanks to the AI's stupidity: I took four melee units into battle, put them in a corner, and the enemy just didn't charge.
As a result, we exchanged unholy/holy words for a long time until he ran out of mana, and the remnants of his armored units were finished off by my resurrected vampires.
I barely had enough mana. I barely had enough spells. And that's after I "cleared" a path for myself on the map at the beginning to find a decent build. I can't imagine how to complete it blindly (relying on the god of randomness, who might give you defense instead of spell power).
P.P.S. In the second mission, I also defeated the final boss.
I only took melee units into the siege and holed up in a corner; the enemy didn't come out from behind the city walls, and I slowly took him down with berserkers and summons.
Otherwise, he was too tough.
P.P.P.S. Yeah, this orcish quest is just a huge pain