Actually it seems medieval armies knew very well who was on their side, even if fighting with people of similar local, faction etc.. The area in which you live is one place that in a small geographic area there is a great deal of fighting between towns, cities and local lords that easily looked alike but there are few accounts, I know of none, where they accidently kill friends. The lack of friendly fire occurs because you often could see the person you were killing. You stayed in a formation. The idea of mass one on one conflict may relate to early medieval but by the high and late period is not true. Medieval armies were in groups. Only if you left your group would you face a high likelihood of being killed by a friend and that might have been intentional for fleeing or breaking.
About them being bloodier.... I do not know if that’s true really. There are loads of battles with very few casualties. I guess with the introduction of bombs, mortars, mines, etc war got far bloodier. Not to say medieval war was not bloody but I do not think it that straightforward.
There ain't nothin' girlie about a tunic...