It's rather hard to force the player into having a balanced army. Why not limit yourself, "houserules" so to speak.
Or why not simply buff lords/monarchs to have much more high tier/elite troops, with fewer mid-low; monarchs ESPECIALLY. I've probably said this multiple times, but I think it's just too easy mid-game.
@Mangoodeye
Go fight the swadians, specifically the Queen with ANY number of Dargas and Keshiks. The first thing she sends out is an armored wall of Paladins, Earls, Knights, Blademasters, and Elite rangers. Tell me when your party of 42 manages a single casualty against the opposing.
Of course, you could fight the Dark Knights for a challenge 10x greater.