I think part of the problem is that steel plate armour should be really good at defending against cut weapons (No sword is ever going to pierce/cut through the plate itself, only gaps in armour), but bashing weapons will still transfer most of their energy through. They also should take some punch out of Hollow Point rounds, while FMJ pierces clean through for the most part.
If you wanted to be wholly realistic while not changing any damage types, plate armour would have something like 40-50 cut armour so not even the best swords can damage through it (but bypass most on crit), but then guns would need upwards of 35 armour penetration in order to go through it.
The real problem then comes in with Kevlar (without ceramic reinforcement), since it is incredibly good at stopping bullets, but can be pierced with a knife.
I think that if we want to go full realism on all of these, we would probably have to change what damage types we use, maybe making pierce near exclusive for bullets and give Kevlar plates special advantages versus pierce.