Revise damage metaphor with a timer. It's timer for how long your PC can last beating on or be beaten by a monster.
Use d20 roll to determine damage
2 no or little damage
16,17,18 significant damage
3 types of damage:
Weapons that pierce (dagger to long sword) do same damage.
Damage should depend more on attack roll. Makes no sense to have a big attack roll that does 1 damage.
So maybe base damage plus amount of attack roll above AC.