Instead of the basic "damage" for everything and the basic Damage resistance that armor provides, perhaps there can be new "Damage Type Modifiers" for each weapon; Piercing, Blunt, and Magical, to be exact. light, medium, and heavy armors would keep the normal damage resistance curve, but along with that, each weapon and piece of armor has it's own damage type multipliers or damage type resistances. Piercing damage could create a raw damage multiplier, but also multiply the opponents DR value and reduce the amount of fatigue damage the weapon does. Blunt damage causes a negative multiplier effect and the weapon does less raw damage, but does more damage to fatigue, gives a chance of knocking opponents down, and negates a percentage of armor value. Magical damage could negate armor values all together, simply being neutral damage.
All weapons could have varying degrees of damage type multipliers, each type of attack for each weapon could receive a certain damage type ratio. For example: A longsword's default attack could offer a more balance ratio between piercing and blunt damage, wheres a thrusting power attack or cleaving power attack would either add a bias in favor of piercing damage or blunt damage. As objects get larger and heavier and higher quality they have a more balanced and higher ratio. Small maces could have blunt force only, but when you get to spiked war hammers they can have quite high blunt and piercing multipliers, and depending on the type of attack you perform, it changes those ratios. A cleave with a sword would be biased more in favor of blunt damage, wheres a stab or thrust would be biased in favor of piercing damage.
I always thought it was a bit weird that an ebony warhammer does like 3x the damage of a steel one. If they used damage type multipliers instead, you could simply give high quality weapons a higher multiplier so they simply perform more reliably and effectively in combat based on the type of armor they are facing, penetrating cheap armor with ease and knocking opponents off their feet frequently. Where an iron long sword would often bounce off of mid-range heavy armor and the user would barely feel the impact, an ebony or daedric long sword will come crashing down on the armor and penetrate it, causing both fatigue damage and penetrating some of the armor causing some sharp damage.
Like weapons, armor could have their own damage resistances. Light armor (or no armor) could be susceptible to piercing damage multipliers as sharp, stabbing attacks easily penetrate the armor, but be resistant to blunt multipliers as users can slip away from the momentum of the blunt attack. Heavy armor could be very resilient to piercing damage as swords simply slip or bounce off their heavy armor, but be very susceptible to blunt modifiers as blunt weapons come crashing down on their heavy armor. If a user wearing heavy armor is hit with a blunt weapon/attack, the magnitude of the blunt multplier will increase the chance of the user losing their balance, and likewise it will make them more susceptible to fatigue loss as the momentum of the blunt attacks cause them to move around in their heavy suit. People more skilled in certain types of armor will gain natural damage type resistances while wearing the type of armor they are skilled in. A master of light armor will easily be able to duck and dodge and spring off off blunt attacks, while still being resilient to sword attacks, and masterful heavy armor user has a good sense of balance and agility so they will be almost entirely resilient to piercing damage, and they will be able to retain balance when being hit with blunt objects better than before.
The general idea would be to give each type of armor it's own benefits that the player can use to their particular playing style. When fighting slow moving, brutish opponents, agile sword wielding characters will need to focus on fatigue-draining attacks and aim for weak points or unarmored areas on the person's body, whereas the slow brutish opponent will need to focus on sharp, piercing attacks to fight the agile and lightweight opponent.