What about giving them 3
adepts, mages and archmages but with no free promotions and double or triple
cost? It makes some kind of sense that training an adept who is also a skilled horseman would be much more expensive. Might be fun as well to allow them to upgrade to knights. 
Some other drawback might be needed as well, like making them a national unit, or require more resources.



Some other drawback might be needed as well, like making them a national unit, or require more resources.