Balanced Units - A minimal balance mod for units

The point of the mod isn't to balance the units of different factions, but to balance pairs of upgrades.

That's understandable. But why create new overpowered units? If in-game balance isn't important at all, they could have just upgraded archers to the level of marksmen. For example, give them 5-11 damage. It's obviously much better to balance units in pairs, based on the unit that's already balanced.

A strange, somewhat "tanky" unit with a clearly defined offensive skill, "Charge."

It's not the unit that's tanky, but the faction. The Kshatriyas have much higher offensive potential, but it's difficult to realize it with an academic because of their low attack and defense stats. In most late-game battles, mage troops try to survive, not attack. And Rajahs fit into this better, with slightly more HP and they don't take as much damage in return.

...either from bottom to overpowered, or from overpowered to bottom.

You're wrong. Are you saying that dancers are a weak unit? Compare them to other level 2 units: zombies, gargoyles, demons. They're definitely not an underdog. I'd say they're stronger than many. I don't remember anyone complaining about them before alternate upgrades appeared.

The same goes for the Elves. They were one of the strongest units at their level. It's just that the Elves that appeared in Warlords of the North were made ridiculously overpowered.

GS are good for breaking through with machines.

I agree. They are indeed good for early breakthroughs with machines or chaos. But not better than warriors.
+5 to defense is -20% damage. Warriors need to move 2 squares away to get the same effect.

First, try to cluster the enemy around you to deal massive damage.
Second, demons are positioned as slow meat. So initiative isn't an option.

Do you think that if you increase the explosion damage by 3 times, someone will cluster together?) It will just be another unbalanced ability. 30 demons explode, dealing about 300 damage. Is that okay? How do you break through them?
With 9 initiative, they won't become fast meat, just a little faster than the older ones, which will increase their appeal.
As an option, you could give them the unused ability "flame of vengeance," I think. An explosion upon destruction of the stack. It was planned to be given to priests. But here, too, the question arises of how to break through such demons.

Isn't it emphasized, though?

The damage of black dragons is noticeably higher: 45-70, compared to 45-60 for red dragons. And burning is too situational. It's somewhat reminiscent of the demon explosion. It's very difficult to use.

And I like it.

I like it too. Yes, it looks logical. But nomads also had their initiative and damage increased.

Added 15 minutes ago

Aren't druids and mages a problem?

Not as much. They have relatively low initiative, which gives you the opportunity to counter them. But Daughters have an initiative of 12. They move before most key stacks. Even a hero with a keen mind might not be able to move earlier.

It's quite easy to break through them as neutrals... their combat potential is weak, which puts them at a disadvantage compared to Daughters of the Earth.

It's easy to break through both of them.
I wouldn't say that Daughters of the Sky are weaker. They're just more difficult to implement and less useful in breaking through neutrals.
But in the final battle, it's not so clear-cut. If they gain level 2 rage, they tear faces off with their chain attack. At level 3, the damage from the chain attack is generally insane.
If you take Secrets of the Light, you can cast chain attacks right away.