Oooh, very interesting. Would love to hear more about this if you get it up and running.
As a suggestion, the way combat was designed was to get an even split between miss, hit and critical (with the very occasional critical failure). You could do three levels of damage and merge this into one roll so:
- Miss = Minor damage (weapon damage at disadvantage)
- Hit = Medium damage (weapon damage)
- Critical = Major damage (weapon damage at advantage)