The only "nice" thing about medieval warfare compared to modern warfare (ignoring greater offensive technology) is that it was less ideological. In medieval times, a battle could be avoided by instead, the two commanders dueling each other and the winner is the one true king or whatever. That's inconceivable in modern times. Like imagine Hitler challenging Stalin to a duel and the winner owns Eastern Europe, that's just so silly! But I wish that was actually the case, because a duel kills far fewer people than a battle.
There were also friendly rivalries and often respect for the nobles you wage war against. Again, that's not really the case in modern times. The USA has never respected any country it just fought a war against, regardless of the outcome. Foraging was devastating in medieval times, but medieval armies wouldn't take reprisals out on peasants based on what the nobles did, for they were just peasants. Nor was ethnic cleansing common.
And that's because views on what a country is are fundamentally different now than they were back then. Back then, kings was where power lay, and the lands they controlled was their personal property to be used or transferred or sold as they saw fit. That's the origin of sovereignty. Nowadays, a country is about the nation of people who live there, and the rulers are ideally figureheads who represent the nation's interests. The horrors Nazi Germany inflicted only make sense in a post-nationalist context.
Overall though, medieval warfare was still horrifying. Hell, off the battlefield, medieval warfare was tragic due to disease and famine and exertion and other stuff. It was even worse than modern warfare in that regard. And anything relating to King Arthur or songs are made-up fairy tales. Judging medieval warfare based on Robin Hood would be like judging WW2 based on Captain America.