Time to get a horse archer only army. Farm Adventurers from taverns and Rogue Blackheart Squires from bandit parties and train them to their better selves. Fill the remaining slots in your party with strong foot archers. And win against all odds using terrain advantage!
I.e. initiate battle near mountains, among the 3 available, choose the map with the closest/steepest hill, plant archers in the top third of the cliff, horse archers at the bottom, order them to dismount horses in a double layer line between you and the enemy to form a horse barrier, make them join the archers close to the top of the cliff, form 5 rows with both. Preserve ammo (hold fire) between waves. Retreat when completely out of ammo and repeat.