We know personal skills are not that important in a medieval battle. Discipline was one of the two crucial aspects of almost all medieval battles, the other being numbers. In fact, this is something Stannis acknowledges as well.
Romans usually tried to withdraw and regroup when they lost formation. Their formation, a.k.a, discipline enabled them to conquer 60% of the known world.
Of course, there are many exceptions. I bet the most classical example is Battle of Keresztes, where the Crusader army routed the Ottoman army but repelled by the military logistics group, i.e., cooks, pages etc.
In this era, there are so many fabled elite units, famous for their discipline. The obvious example is Polish Hussars, while Swiss Armored Pikemen are just a little behind. If we intend to extend the list, Janissaries, Tercio Pikemen, Varangian Guards and Catapracts would come next. These elite troops were to rally routing troops, keep formation, break through enemy lines etc. None of these tasks could be performed by peasant levies.
However, with the exception of Kingsguard, there are no elite troops in Westeros
This is not specific to Westeros. The only elite troops we have heard of in Essos is Unsullied. It seems like no one in Planetos cares about elite troops. In fact, it is even worse for Westeros. How does Kingsguard fight in formation, where discipline is way more important than combat skills? It feels like seven thickly armored troops would jeopardize the entire regiment.
I am not suggesting they are useless. They may be used to break the formation (as much as seven men can do), reach and kill the enemy general or protect their own general. Their primary purpose is protecting. We also see Kingsguard represent the king in his absence.
Now comes the single combat part. If the enemy general, without loss of generality lets call him Rhaegar, were to face single combat with the allied general, who shall be called Robert, where are the Kingsguard? Of course, this is apart from those protecting someone else, who we shall name Lyanna. If the single combatters are not generals, i.e., two prominent knights, do the rest of the troops around them stop fighting?
It feels like warfare in Medieval Europe is quite off compared to warfare in Westeros, or Planetos in general. The final part of my question is if we know any famous single combats in battlefield in Medieval Europe.