For instance, watch the Smough and Ornstein fight here: https://www.youtube.com/watch?v=Pyv2bcbxRA0
Any one of those hits ought to kill him instantly (and some come close), but keep in mind he's naked and SL1 and your lifebar goes down about that much if you're level 65 and in stone armor.
Or watch this... https://youtu.be/PUHJ90zZETA?t=7m14s
The last boss fight. He probably isn't that high of level.
Also the fact you can run past most enemies in the game seems problematic to me (although an issue with many action-rpgs).