What kind of magic do you like?

You only need to conserve mana in battles against neutral creatures; why save it for the final battle? It's clear that you need to use cheaper spells, but only when you have enough of them.

I agree. The final battle is a completely separate encounter. However, most battles – practically 99% or more – take place against neutral creatures. This is why there's so much focus on battles with them. Here, you need to think, optimize, and decide which school to develop for the final battle, taking into account how much it will help you overcome the mass of AI opponents.

The same third-level magic from Nature or Life can be much more effective than Chaos magic, but that's all subjective. But in my opinion, a summoner is still more useful than a charmer, and their creatures deal more damage if there's nothing to eliminate them.

The last point is also quite subjective and niche. Summoning is an excellent school, but it's not universal, while the Order school (I repeat) is universal.

Chaos seems too easy, especially against the AI, because it's so straightforward. And it hardly shows itself in defense, since all its buffs are for offense.

Isn't Life also bad because it focuses more on defense and is weak in attack?