well it is like this today too. you can have superior tanks for example but if you send them unsupported by infantry or artillery charging straight into enemy army which is dug ind and has made obstacles and put mines in front of their positions then they will not preform well in that battle.
at Nicopolis Crusader army (French , Burgundians) did just that. their heavy cavalry rushed straight into Turkish army without Hungarians which were left way behind. Even when they (Crusaders) saw that charge is impossible due to obstacles that Turks dug in front of their lines they continued with the attack dismounting and proceeding on foot under heavy fire. and this ended in disaster.
as you can see it was lack of discipline and reliable command structure that was a big disadvantage of most European armies.
when Hungary employed a large number of disciplined mercenaries they did much well in battle. Today mercenaries have a bad name "dogs of war", but at those times they were closest to professional modern soldiers than any other branch of military.
When a big army assembled with more than 10,000 troops it was heterogeneous made of various nobles from around the country and their contingents which were almost impossible to command in battle. so much tactical plans drawn before battle were ruined by some fool who could not keep his nerve and charged the enemy when shouldn't (Varna).