How the Damage Model can be made better
A good armour damage model needs to achieve several things:
-Armour needs to feel like armour and not cardboard. High quality historical armour provided a huge amount of protection from most strikes and the gameplay needs to reflect that.
-Incidental, weak blows should do zero damage.
-A lone armoured combatant should be brought down by dozens of peasants/looters. In real life, a lone knight would be wrestled to the ground by the peasantry and knifed through eyeslits/armpits or had their armour undone before being killed. We don't have that in M&B, so it's important that such attacks from low-tier fighters still do ~1-2 damage so that lone knights who lose their horse amongst peasants can eventually be killed.
-It's important that the armour doesn't absorb too much damage from super heavy attacks - like trebuchet rocks or a lance to the face from maximum velocity.
-There should be a meaningful gameplay distinction between using Cutting, Piercing and Blunt weapons. The player should find themselves in situations where they have to weigh up the pros and cons of which item type to equip. There sort of already is a distinction between cutting and the other damage types, but ideally there should be a distinction between piercing and blunt too.
These goals can't be achieved by either an integer damage reduction or percentage absorption system.
Instead I propose a piecewise function - something that absorbs all damage from small attacks, lets some damage through for medium attacks, and allows lots of damage to get through from heavy attacks.
One way of doing this is with three joined linear functions - a flat damage reduction up to some value (let's say armour/2), a small amount of damage leakage (say ~25%) up to the armour value and full damage for higher values.
Another way is to join a curved function (such as a parabola) with a line. You just match the two up where the curve's slope becomes 1. A more aggressively curved function like a cubic or exponential could be used to further reduce the damage at low levels.
This gives more room for mixing and matching models to make pierce and blunt damage a bit more distinct. For instance, armour could be more effective at absorbing very low damage pierce attacks vs blunt attacks, but less effective at moderate damage levels.
Alternatively, blunt damage could be more effective at interrupting attacks. Currently all damage types will interrupt an attack if the damage dealt is over 5. If the threshold for blunt damage is lower, it allows blunt weapons to be more threatening to armoured opponents without necessarily having to be completely armour piercing.