I know the table might seem ruthless because scoring a critical, or being damaged by a mid level caster can easily deal over 20 damage in one hit.
Hell, I know it did not come easy when I got that 40 damage and could not use my left arm.. and later on, the foot because of damage inflicted on me.
But nevertheless, it does not matter if you like it or not, it makes sense comparing it to real life. If you think about a real karate style fight, you take one good punch/kick into the head and you are unconscious. So, receiving one critical hit with a greataxe for example should cause a serious impact on the body.
One thing though, the Fort DC equals damage inflicted? That is a lot! Why not set it as 10 + hit dice of the wielder/caster + main stat modifier of the wielder/caster?
(E.g For a hit from either Sladan or Annien the DC would be 24 at level 9, not maybe 30 like a possible damage)