Two sisters.

Regarding the map, why is the AI developing so strongly? The developers were able to control its development in missions, and scripts and functions handle this perfectly... or am I mistaken?

Here, "stronger" means something different. First, the map is oversaturated with various enhancements. Second, each hero company starts with medium and large stat bonuses; plus, each hero has a large number of good artifacts. The "behavior" is customized for each of the Grimheim factions – each is busy with its own tasks, some clearing the map, others building cities and scouting. There are more resources on the map, again, plus a large number of gold mines and dwellings with creatures.
As a result, after two months of gameplay, the AI usually captures 3/4 of the map, develops to its maximum, and fully builds all cities. Then it simply starts buying ALL weekly reinforcements. Usually, it makes every other hero "main," while the rest carry reinforcements to it, i.e., 6-7 heroes with constantly replenishing armies run around the map and collect all possible bonuses and spells. And when, finally, a particularly slow player decides to attack Grimheim, they will face a very harsh reception, and these are Knights, not Dark Mages, plus they have a minimum number of enhancements in their starting zone, and it's difficult to reach a high level. And while you will have only 20 Archangels, the AI's six heroes will have two to three times more (Dragons), and they will also have superior stats. Even if you defeat three enemies, the rest will overwhelm you with numbers.
I'm not arguing that, in the end, everything will even out. And the AI will stop developing so quickly and simply sit in the castles, accumulating an army. But it will be impossible to defeat it there. I hope I explained it clearly ;)

Suggestions: make more maps in the same style – that is, the player's Castle in a box of walls with a guard post – I love playing defensively!
I also want to suggest fewer bugs and a full-fledged campaign.

Well, this doesn't entirely depend on me, unfortunately; 99% of my maps are unfinished, so it's hard to promise anything. But still, thank you, we will try.

And now, criticism – please! Don't strain my eyesight... orange or yellow on a white background is terrible for the eyes((( make a more gentle color).

My task was to create a blizzard; at worst, a dense fog. Perhaps, if it's so unpleasant, I will add a separate version with normal lighting. However, it's already normal in the Dungeon, or rather, as usual. Almost.

Added 3 minutes ago
And also about the AI's development – I said that, in general, for a map of this size, two months is usually not enough, but in this map, the computer manages to develop fully without problems – the large number of cities and upgraded heroes have an effect.