I think that headslashing someone is as hard as headshotting, because aiming for the head in combat prevents you from seing most of the attacks.
Im not saying your WRONG but in my experience thats NOT so. And please dont take offence when I ask the following, and when I give 3 tips:
Question: How long have you been playing?
1 tip: To direct your block OR attack, it only takes a tiny movement in that direction on your mouse, and instantly after directing you can redirect your view/aim.
2 tip: I honestly can't remember what default is, but you can set the direction you are attacking/blocking to be visible onscreen with small arrows, try this if you havent.
EDIT: I have never used this but I see it in ppls youtube stuff etc, maybe it helps them I dunno.3 tip: Despite where you AIM an attack, you should keep in mind (and eye) the animation; truly an amazing part of m&b, the weapon model shows greatly what angle/point your weapon is moving from and to: you wont always hit exactly what you aim at, and the left swing of a left hander as an example, will hit your opponents head very easily.
All this I type because offtopic, just because I think hitting an enemies head is not that hard in melee, but even though I spent about a dozen generations (Over a year for me, cause Im slow grinder) as an archer on my main I still find it hard to headshot ppl with an arrow
... Guess like most things, its pretty subjective.