Necropolis and Demon.

Therefore, you need to eliminate the Necromancer starting from the first month.

By the first month, the Necromancer will have a decent army, and defeating him will be quite difficult. You can't just rely on Imps with mana. First, the Demon will have to work hard to gather a reasonably suitable army. This means he'll have to take Dael. Meanwhile, the Necromancer will capture some Sulfur, build a Castle, and sit in it. Capturing the Necromancer's Castle is much harder than capturing the Demon's Castle, especially if the Necromancer has a spiritual connection. I don't understand how the Demon can easily defeat the Necromancer in the first month. Unless he attacks in the first week.

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And the Necromancer faction is far from the strongest. Since Heroes 3, they seem to have been strengthened with abilities, but their overall stats aren't that high, with average defense and almost zero attack, especially for Dragons, which frankly aren't worth the resources spent on them.

My friend, you clearly haven't played Heroes enough to reason like that. It's well known that Necromancers rely on quantity, not quality (although, looking at it, what's so low quality about them? Just consider the cost - how much do Messengers, Liches, and Vampires cost!). Yes, the Necromancer's attack is weak, but that's not a problem - there are artifacts, magic, and other options. You can gather hundreds of Dragons, Ghosts, Skeletons, and Zombies, and you can gather thousands of them if you know how. And gathering several hundred Vampires, Liches, and Banshees is also not a problem. And what about the magic, what about the Phoenix, so many development possibilities. So, you're wrong to criticize the Necromancer faction.