What's unrealistic about an all-horse-archer army? That's pretty much what the Mongols were and they were surely the "ideal" army to have during the Middle Ages, certainly the most effective.

Admittedly 10 Polish Nobles is pushing it a bit... but I wasn't trying to suggest a realistic army, merely an effective one. I did also suggest a realistic army which I do try to use, but as I pointed out it's expensive and not very effective so hardly ideal.