How much of an impact did individual skill and troop training, or maybe battle experience, have on the battlefield? I'm not talking about tactics, such as shooting at the enemy force before the two armies meet, but what happened when the soldiers crossed swords with the enemy. If an army of 1000 met an army of 2000 in close combat in a flat open field, and both were armed and outfitted the same, could any amount of skill or training overcome such a large size difference? Does the answer change if you scale it up to 10,000 vs 20,000? I understand that combat was somewhat avoided when it could be due to it usually being a matter of who had the larger army, which is where this question comes in.
Edit for clarification: I am counting close combat tactics as part of training, just nothing that would lessen one force or the other before they clash, and nothing that relies on specific terrain since my scenario has flat open ground.
Take my words with a grain of salt, I'm not an expert on the matter.
Medieval warrior skill generally played only a small role in combat. Medieval warriors, and most warriors up until now in fact, performed combat in a group. Platoons, legions, regiments, squads, etc.
The three deciding factors in a battle were typically not individual skill, (though it helps) but terrain, equipment, and leadership.
Control of the high ground, resources/equipment of your men (usually not with much variation - peasant levies were common up until 1300, though it's debatable when the levy system ended.) were less important than leadership, usually.
There are many sources that imply that lesser armies can take on superior ones, for examples -
https://en.wikipedia.org/wiki/Battle_of_Halidon_Hill
Weapons and Fighting Techniques of the Medieval Warrior - Martin J Dougherty
The Medieval Warrior: Weapons, Technology and Fighting Techniques (Revision of above, I believe.) - Martin J Dougherty