I would say it is the opposite, center hits are more likely to hit a flat area, reducing the chance of deflection with minor damage, which is also a reason that plate armor was rounded. There is also human bone structure, your sternum and ribs would receive the most out of the impact.
Those are two videos from Tod's Workshop:
Medieval Crossbow vs Flexible Armours
ARROWS vs ARMOUR - Medieval Myth Busting
As a bonus:
Lockdown Longbow - Do shields stop arrows?
Because blunt based weapons are not meant to pierce the armor, they are meant to transfer force through the armor into the person wearing in. What would help negate the effects of blunt weapons to a degree would be flexible armor (chainmail, for example) with increased padding, like wool, leather or a gambeson underneath.
What Kind of Damage Can a Medieval War Hammer Do?
Medieval Crossbows vs. Breastplate and Lamellar Armor
From what I've seen, those mods change values that translate the individual skill of each individual model in the unit (which in the ends translate to the unit effectiveness). Like increasing defensive values and reducing offensive values, so units have less chance to cause damage to each other, thus requiring more attemps to be made before killing a model.
This is something that can be translated to Bannerlord by increasing the AI effectiveness by skill points, it was like this earlier on but then reduced once people started to complain that they were having a hard time dealing with npcs on tournaments, lords were hard to take down, which then reflected on the combat AI becoming dumbed down. And by skill increase I mean something more along the lines of prioritize staying alive instead of mindlessly hacking away trying to kill everything in their path and becoming more effective in killing as they progress in tiers.
I would argue that an Empire Legionary should have quicker reactions than a recruit, enough so that they are better fighters by being more skilled and not simply by having a higher armor rating or being able to take more hits. The disparity between skill levels should be increased.
The experience required to level troops and the cost would also need to be increased, as a form of balance and avoiding fully elite armies steamrolling everything. Which in turn would result in armies composed of a greater number of cheaper, less skilled troops that would take longer to kill each other.
This of course would mean that players would have a harder time facing elite units and the complaints about the player not being the T-800 that people expect themselves to be would increase.