There is a problem with armor piercing: to pierce armor well, you need a lot of one damage type, as each damage type is applied separately.
For example, a nodachi - with its huge (50) cutting damage, it pierces armor well. Against a plate armor (16/16 armor), it deals 34 damage - 62% of its 50(cut)+5(bash) damage.
Meanwhile a war hammer - weapon specifically intended for armor piercing - deals 20 bashing and 20 piercing damage. Against same plate armor, it deals meager 10 damage - 25%. That +2 comes from piercing being very slightly better against armors than cutting.
Instead of dealing the attack essentially as two separate hits, it may be possible to deal it as one, spread across the armors.
Using the example above, a plate armor would have a protection value of 16, with multiplier of 100%/100% for both bashing and cutting. A nodachi has 50 cut and 5 bash, meaning it would count as 9% bashing, 91% cutting weapon. Since for plate armor the values are identical, it would just tank 16 damage - 55-16 = 39. Thus dropping damage to 71% of its initial value.
For war hammer, it would be a bit more complex: plate armor has multipliers of 100%/80% against bashing/piercing. Since war hammer is 20/20, this would mean the average protection multiplier is 90%. Thus the armor would offer protection value of 14.4. 40-14.4 = 25. 63% of initial value.
But then there are critical hits and those have their own armor multipliers:
Bashing ignores 50% armor on crit
Cutting ignores 5 armor AND THEN 25% armor on crit
Piercing ignores 34% armor on crit
In current version, this means that:
A nodachi against plate armor deals (before damage modifiers from crit): 0 bashing (5 - 8 < 0), 42 cutting (50-(110.75)=50-8). 76%
A war hammer against same plate: 12 bashing (20-8), 11 piercing (20 - (160.80.66)) = 23 total. 58%
In the “one hit” version:
Nodachi: bashing multiplier 50%, cutting multiplier: (16-5)/1675%=52%. Nodachi ignores ~50% armor, deals 55-8=47, which is 85% of initial damage.
War hammer: Bashing at multiplier 50%, piercing at 53%. War hammer ignores ~50% armor, deals 40-8=32, which is 80% of initial damage.
From the change:
Nodachi would gain +9% damage against plate on regular hits, +9% damage on crits
War hammer would gain +38% damage against plate on regular hits, +22% on crits
While nodachi still ends up more powerful here, it gains less than the war hammer. Later we could adjust all armors to the new power levels. Then nodachi would become less good at armor piercing than dedicated armor piercing weapons.
tl;dr Deal whole attack as one against armor, instead of splitting it up into two and applying armor against each