Auto-translated
I think that if there were a fourth column, it should contain random creatures from other factions.
Here's why:
Arguments:
1. Perhaps these are mercenaries, but then each faction would need to have specific restrictions, for example, for the human faction, demonic creatures could not be hired in this column, and so on.
2. This would make it possible to profitably purchase heroes of other races as full-fledged commanders.
3. This would allow you to create a fairly powerful army without capturing castles of other races; for example, Zealots and Elven Archers are quite powerful together.