That's not it at all. Armor and tight ranks are really, really good at keeping people alive right up until gunpowder weapons.

It was entirely normal for armies of several thousand people on each side to clash and have <1% casualties for an hour or more. And you can tell this is not because of some ceremonial reasons because of what happens when ranks of one side finally break, because then the side that manages to hold cohesion will absolutely slaughter the losers.

Go watch some videos of modern melee tournaments where the participants are in full armour. Armoured combat essentially turns all weapons into blunt objects unless you manage to get a point of a sword into a gap which is hard to do while being pummeled over the head.