I can create a version where 1 player faces 4 in an alliance.

In my opinion, this map has great potential as a “single-player” map. It’s too large for “multiplayer.” The presence of a super artifact and a very beautiful landscape aren’t that important in “multiplayer”; it’s more about the balance of power. To create a high-quality “single-player” map, it just needs a little more work: allow the player to choose one castle, and give the remaining castles to the computer with an easier start, perhaps by giving it heroes with some pre-defined skills for development.