AI heroes are afraid of each other; one strong hero is afraid of a weak one, and another is naturally weak.
The difference is significant.
Is there anything that can be done? The gameplay suffers.

Is the problem in the ND mod or in general? If it's in the ND mod, then it makes sense to write in the topic about the ND mod; no one here will help you.

If it's in general, then over time you will understand that the entire gameplay is lost in a game with AI :D And there is no point in it. Unless you want to compete with people to see who can kill it faster on a given map or starting save.

Added 5 minutes later

How can I defeat the ranged dungeon and castle? The creatures approach and lie down from direct shots.

For a question like yours, the following data is needed:

1. Template.
2. Size of the generated map.

This is mandatory.

But everything will still come down to the phrase "learn to play."