This is my opinion how the damage types should work:
- Cut: Useless against plate (mostly glances, only little damage if no glance), somewhat useless against mail (medium damage, still glances sometimes), normal effect against cloth armor
- Pierce: Somewhat useless against plate (mostly glances, normal damage if no glance), normal effect against mail and cloth armor
- Blunt: Normal effect against all armor types
This would of course buff heavy armor a lot. I don't see this as a problem, as heavy armor costs a lot and slows you down quite noticeably. It would of course lead to more tincans on the battlefield, but this is not negative in my eyes. It's already very rare to see something heavier than transitional armor.
It would also change the weapon distribution. People would flock more to blunt and pierce weapon types. The times of the Kuyak-clad DGS swingers would be over. A new era would begin.