Ideas and suggestions.

2Qwertyy - of course, it's impossible to play large maps without Earth and Air, and even with your changes, Water clearly won't become a skill that a hero will take on them.

Pridu, it's not just large maps. Shield, Stone Skin, and Slow all help in battles, even in the early stages. Poop/Resurrection/Implant are useful for breaking through a Guardian or capturing a Utopia.

You don't need to take Water just for the sake of Water. It should remain a support school. And therefore, it should synergize with classes that are focused on combat with their troops. And these are Warriors.

If a Warrior has Expert Leadership and a Medal, then he has +2/+2 to combat stats and morale. Ice Armor gives +4-6 armor, plus improved healing. And so, a Warrior can take all the objects on the map without taking Earth at all. He will just have to endure a little in his stacks, as is his role.

For Guardians and in difficult battles, there is the strategic Ice Ring to slow down a couple of stacks. In a battle against a Mage, there is Anti-Magic (which will be in all schools), as well as the need for the Mage to develop Magic, Water, and wear artifacts that reduce morale. Plus, the Water Mage will have at least some control and mana reserve.

All of this should work together to improve the Warrior class and make Mages more Mage-like. The goal is not to buff Water to the level of Earth. Not at all!

There should be 3 main hero archetypes: Warrior, Mage, and Battle Mage. Right now, there is only one of the latter. And he definitely needs Earth. Without it, the game will be a pain on any map.

There is also a 4th class - Support. This is a hero who should be playable with a set of skills: First Aid, Artillery, Mysticism, Logistics, Eagle Eye, Estates, Diplomacy. There are also ideas here. But there are also problems. I don't know if anyone is interested in reading about it.

In general, the main principle of good balance is to balance specifically by archetypes. So that several skills together make a hero competitive or at least playable in some moments. Trying to simply buff individual, completely different skills to the level of the strongest, or vice versa, to nerf/rework strong skills to the point of being unrecognizable, is a path to new problems and failures.