What's the difference between choosing different mages?

For the Mage Guild? The difference isn't significant. If you take a Necromancer as a dark mage, they'll have one extra spell and a Lich to sell. If you choose a simple Elf for summoning, they won't have top-tier nature spells.

The eternal problem of morale in the ranks of troops.

However, combining troops from different castles creates stronger builds. You can also play by using an army from a single castle.

It's a bit inconvenient that experience isn't gained for completing quests, like in an RPG.

Experience for quests would disrupt the integrity of their realism. Besides, you can normally reach level 33-35 by the end of the map.

Perhaps, even by simply reducing army sizes and growth rates by these same 10 times, the game would become more dynamic.

I agree with that; there are problems. I tried to adjust the growth rate coefficients to match the average playthrough, but they vary greatly; some people finish in a year, others in three.

At the same time, the role of Chaos would increase.

I personally tried playing with Chaos; of course, you have to put in the effort, drink magic potions, and attack several times, so you can't use it normally in every battle, but only once a week, but you can deal 5-7 thousand damage before the battle.