Heroes 5.5 WarGame Edition - Tactical Edition.

Although, in the realities of WGE, the "Hive" and "General" might be just as effective as "Chaos" when it comes to casting spells. Simply because of the cost, an Elf won't be able to afford to cast a "Rain" spell and then follow it up with a barrage of meteors. However, the cheapest spells costing 1-2 mana are perfectly suitable for "Rain" (and area-of-effect spikes and fireballs are still available to the Elf even without native "Chaos" magic; in WGE, "Fireball" is a tier 2 spell). Due to pricing, the policy is that top-tier tier 4-5 spells should be cast only a few times per battle (and even gathering enough mana for a single such spell requires effort), while low-level spells are cast much more often due to their low cost. But the power of top-tier spells will be worth it; increasing their cost is not just a weakening, but rather an enhancement of their power. In other words, there will always be plenty of mana in relation to low-level spells, but a severe shortage in relation to top-tier spells. In WGE, 1 unit of knowledge grants 5 maximum mana (not 10), while tier 1 magic costs 1-2 mana, and tier 5 costs a whopping 20-30. For example, "Armageddon" costs 30 mana, so you'll have to spend 6 knowledge points just for one use :) Considering that stats are valued twice as high in this mod (attack and defense provide twice the bonuses, and magic stats are in the same balance), it can be said that this "Armageddon" would cost as much as 120 mana in terms of the original game. Although, for penetration, it's 60 mana if you look not at the maximum mana, but at the speed of its regeneration.

Added 19 minutes ago

What about caster-mages? Low-level spells are cheap, high-level and mass spells are expensive. Some casters have both mass/high-level and low-level spells. Should we give them a lot of mana so they can cast a mass spell at least once? But they could overwhelm with 1-2 mana low-level spells.

Maybe just reduce the mana from Knowledge? Not give 10, but less? This is quite adjustable.

It's already been reduced from 10 to 5. And what's the problem with low-level spells from casters? Let them overwhelm as much as they want. It's like the shots from archers. The main thing is that they don't overwhelm with top-tier spells. The composition of spells in caster spellbooks will be such that tier 5 and tier 1 spells will definitely not be in the same spellbook. The maximum number of spells a caster can have (in terms of quantity) is 5-10 tier 1 spells. But it's more interesting with "Secrets of Light," because 1-mana spells will most likely become free and, accordingly, infinite (just like for the hero under "Tactical Supremacy").

Added 10 minutes ago

By the way, in the executable from 2.1, it was possible to set "General" Overseer as a buff, after which the ability was lost.

No, a mass "Overseer" is not interesting because it's no longer an activated ability. But another "Overseer" is interesting - a tripled one (in other words, the Human "Tactical Supremacy" will replace the regular "Overseer"), especially in conditions where the hero's damage is good across all tiers, and not just tier 6-7. The trick of "Overseer" in penetration is to motivate the player to expose the "Overseer" stack to attacks from neutrals (and not the entire army under "Overseer"), and with a triple "Overseer," this will be a powerful thing. And in the final battle, using "Overseer" will effectively give the buff "attacking this unit in melee combat is more expensive for them; it's better to leave it for later."