Cambridge History of Warfare touches on some of the media stereotypes we see in this. Knights in armor were expensive and logistically difficult, and the historical narrative is only dominated by these tales because they were being written by nobles. The idea that a man in armor is a force multiplier is pretty much a myth; French knights tried to defeat the Flemings at Courtrai in 1302 and lost nearly a thousand men to militias and upper class burghers using pikes and spears. It doesn't help that Cortez lied through his teeth about killing Inca armies twenty times larger than his own party because it made it seem like guys in armor always win. They're like Tiger tanks- slow and heavy.

In reality, medieval warfare followed a pattern similar to Roman times- men stood in a line several rows deep with spears. Archers attacked with volleys to soften an enemy advance, then the spears (typically taller than the guy wielding it) went forward and stabbed at the enemy. Long spears are very good at defeating cavalry charges. If swords were used it was because the pikes had failed to keep the enemy at a distance.

The key to this battle style is discipline, because once you break the line it is very easy for the enemy to break up your offensive mass and whittle away at you- cavalry is used often in this period for flanking attacks for this reason. If your line breaks you can have a wedge drive deep and push you away from your comrades, letting soldiers into the gap. This is what cost Godwinson at Hastings- when his forces stepped out of formation and chased retreating cavalry, the cavalry doubled back and hacked the foot soldiers apart one at a time.

So yes, poorly trained troops die easily in European style warfare, because training and discipline is really important. But the armored knight's role is overinflated because the only literate people writing about military campaigns were officers who often were egotistical.

Hope I got all that correct, leafing through my copy right now.