Would be fun to be able to have one hero in each class for battles, and let he commander doing the rollcall decide which of them should be accepted. Guys making armies would be able to field all cav armies, or whatever they would want for a battle, depending on what gear they would have bought in advance.
HA mongol style? No problem
30 english longbowmen in the same team - no problem
All piker army to counter an army known to be all cavalry
And if u definately wouldnt want to play as HA for instance u wouldnt lvl that charactr and the commander doing the rollcall just wouldnt chose him.