I don't like arguing, but I didn't mean "equilibrium," and I've never played it. The map was L-shaped, and I gathered about 80 vampires fairly quickly, although my heroes didn't level up much. There were only 2 of them in the army, and they leveled up quickly, except for the buildings. They were constantly fighting monsters, there were no sacrifices, and the battles only brought benefits. You just go and clear everything you see; you don't even need to think. Although the army is much larger than mine, how can you level up 3 heroes in that time? Even if you do, 1000 mana is a lot, and you still need to level up magic to level 5, which means your heroes won't have any defense and will be defeated with one hit, unless you constantly use potions of immortality, but then you won't be able to cast spells. You also need to consider that I have a Death Knight, which increases the stats of monsters, and the dragons or vampires will reach the heroes in 1-2 turns. Plus, the Necromancer can buff the dragon with Vampire Touch. And if you also get the Sacrifice spell, then it's clear what will happen. You also haven't considered the fact that you might not get that magic; the chance in your city is 1/3, and there might not even be 2 Chaos cities on the map. Even if you're lucky and there are, it's not guaranteed that there will be a Death city. In general, I wanted to say from the beginning that with Necromancy, you'll have many more vampires than if I had bought them in the city, and you won't have that many Chain Dogs to do anything. Most likely, you'll have 5-10 of them, if you're lucky...
1) Even on a Medium map, you can easily level up 5 heroes to level 15.
2) If we're talking about percentages, you only need living units to raise vampires, which means you can ignore battles with undead and mechanical creatures.
3) You can increase the defense of your heroes with artifacts or academies.
4) What's stopping me from taking a Death Knight? As I said, people level up 5-6 heroes and it seems to work fine. And Chain Dogs are much stronger than vampires, even in large numbers, with the Tactics skill.
5) In 1 turn? Well, who would doubt that I wouldn't put my heroes on the front line, right in the line of fire? That's nonsense. In 2 turns, assuming you're rushing.
6) So, you get the Sacrifice spell, but who are you going to sacrifice? Skeletons? That means the army's speed will be 18? Or are you going to sacrifice dragons?
7) Even 1 Chain Dog is dangerous. With 1 Chain Dog, you can defeat neutral creatures up to level 2. And if there are more...
Why don't you post your L-shaped map? I think it's empty, and you're just relying on it.

Барон "Vampires"
Отдай свои прошлые сны,
В сомненьях себя обрети,
В бешеном танце душа кружится!
Не думай, что будет потом,
Здесь и сейчас мы живем,
Стань хоть на миг сам собой, слышишь!