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I'm not voting for anyone. There are no strongest factions (or there shouldn't be).
You can look at this issue from different angles. (I'm looking at it from the player-versus-player perspective...)
From the perspective of balance, the developers should have adjusted everything.
What other advantages could there be? Right, Dark Energy – as an additional boost. But here, the question is whether it benefits the Necromancers more, or is it equal for everyone.
What else could play a role? The summoning of gates by Demons, which can significantly complicate battles against them. But for this, the summoned creatures and the summoners skip their turn – again, the developers are balancing the situation.
What else? Oh yes, the Dark Elves, who can't build a city and can't recruit a large army. If they are supposed to rely on magic, then with long-lasting yearly maps, they should theoretically fall behind significantly.
Regarding the boosts, Dwarves are almost invincible in their own castle, but this was balanced by forcing them to spend resources on runes.
Now, let's go back to magic. Chaos magic dominates at the beginning, Dark magic at the end, with Light magic slightly below, and Summoning magic is unclear where it stands.
Now, about the question regarding Orcs. Here, it's a complete balance-imbalance-player luck situation. If you accumulate more Rage, no enemy has a chance. You can get protection from magic. But no, and this turns into an equal situation due to the loss of that very Rage. As a result, Orcs die just as quickly.
But, we can also turn to AI.
I once created a map where troops were created semi-randomly, and then we moved forward several months in the game, and then held Competitive matches. Everything was fair; each duelist fought another with equal troops. What did I notice? Right, very frequent victories for the Necromancers. Why? I don't know. After all, Dark Energy didn't play a role, and the troops were accumulated only through the city. Dwarves were outside their castle walls and lost quickly. The boost didn't save the Demons; they were killed faster. Orcs won a couple of times but suffered huge losses. Dark Elves only lost all the time. What does this mean? Does the AI command the Undead best? Or is it something else? Indeed, a complex question...