I think most of the people hit the nail on the head.
You say sometimes you take 3 hits, sometimes 7. It's not random, where are you getting hit those 7 times versus those 3 times (head, body or legs, and how much head body and leg armor did you have). What weapon type are they using (blunt, pierce, cut), how much base damage does the weapon do? How much momentum did they have in their swing (speed bonus)? How much power strike did the person have, how much WPF do they have for that weapon type? How much did their armor weigh, bringing down their WPF (if they are lightly armored, they are going to hit harder and faster, faster = more damage by the way also). How long did they chamber their weapon before swinging, if it was .6 seconds then it was as hard as it could hit (assuming max speed bonus), maybe the time you were hit 7 times they held their swings too long or not long enough...
So many variables come into play.