It's hard to make the game realistic yet ba lancet at the same time. Because ... war was never meant to be balanced xD
ThinkING about it , Mongols would bring wagons full of arrows deployed at the edge of the battlefield to resupply their troops . Their horses were lighter which could outrun any heavy cavalry and their composite bows could pierce through armor even from long distances. With these techical advantages alone they are a dominant force in the pitch battles compared to any other army at the time.This was all due to the terrain of their homeland and their war like culture, as well as the prominent people that shaped their history.
And so if we make battles realistic I think we should keep things like geography and culture in mind.
Imagine if we can pick a certain clan that has their own attributes, strengths, weaknesses and army compositions. Along with what everybody suggests so far with the ammo and stamina levels in mind.
Wouldn't that be fun ? But haha I guess I'm image in too much.