I am not sure it has been mentioned before but I think it will be cool if Hero have dual class trait, for example THIEF is Goblin/Rogue, warpriest is Divine/Human, something like that
For clarity, the term you are searching for is “Troop Type” not “class”.
Your Hero is always typed “Hero”. The only mechanical difference this seems to make in battles is the Troop cannot be duplicated (by Doppleganger, etc.).