I agree. Early medieval era was characteristic by lack of tactic whatsoever in battles. The troops were disorganized, basically, each knight arrived on the battle with his group of vassals and conscripted infantry (often peasants) as he liked. The knights did not want to recognize a supreme commander, and though individually often very brave, their tactical prowess was negligible. It can be said that the French lost many crucial battles in the One Hundred Years War (Creche, Azincourt), where a group of well organized archers defeated vastly superior number of French knights (though their tactic was based on passive defense of advantageous position).
But first examples of advanced battle tactics started to appear only in the late medieval / early rennaisance era. Czech hussite insurgents used wagons for both defense (vozova hradba) and offense (wagons loaded with stones to break enemy ranks), also introduced first crude firearms and artillery, as well as modified peasant tools (war flail) to conquer their Catholic enemies. The first footmen that were able to offensively fight against cavalry were Swiss pikemen.
Eastern nations, on the other hand, were much more disciplined and often used advanced tactics in battle. Mongol hordes were able to attack in waves, flank, feint retreats and stay incredibly mobile during long campaigns, and that allowed them to conquer more than one half of Europe. Saladin's troops that faced the crusaders also applied similar tactics to stand a chance against their better armored foes.
All in all, I think that detailed formation control would be inappropriate for the game of this era. The commander of this time could at best chose the initial formation of troops (if he had time) and then give the order to charge - and hope for the best.
