I read just yesterday that somewhere around the sum of just
three English Kings in the middle ages were spared having to go into battle at some point, so being a King was certainly no easy ride either.
Fantasy which makes use of the medieval world (and it usually does) isn't really looking at the true medieval world, which was a dirty and brutal place to live but an idealised version of it. Even the pulp of 'swords and sorcery' stories don't go into the truth of what life was like back then.
Though I'd argue that such a simplistic definition of sci-fi and fantasy is all wrong these days anyway. How to account for Steampunk for example? Genres are collapsing like ninepins, and a good thing too!
