In which city is the alt upgrade more balanced?

Hmm. I disagree with your opinion about the Dark Elves regarding balance (I can't say about the others because I haven't played them much). Are Assassins better than Stalkers? That's debatable. At the very beginning, Assassins are better. When I have more than 50 of them, I transform them into Stalkers. Your opinion that invisibility is useless could only be written by someone who has used this ability a couple of times at most. And you didn't provide any arguments to support your point of view. In my opinion, it's a very useful thing. It allows you to avoid losses when any other race would suffer heavy casualties (especially effective against archers and mages – use invisibility, attack with Chaos, and finish off with the same Stalkers, and sometimes with the help of Succubi). This strategy really works, and not just occasionally, but consistently. Fury/Harpy units are indeed well-balanced. When there are few, choose Fury; when there are many, choose Harpy. The third-level upgrade is probably only useful in specific situations; otherwise, the old one is better. The fourth level is where the imbalance lies! A quarter of the damage to enemies in the path instead of ignoring defense?! What nonsense! The fifth level is not better. Either a tiny 30-50 hit points for each, not very frequent turn of Hydras, or a quarter of the damage with acid when the Hydra is attacked. This is a useful thing, I've tested it. The sixth level is quite balanced; you can use either. And the seventh level is also well done.