I have just posted an update to this plugin that adds in a couple of ways to mitigate balance problems resulting from scaling.
Expertise is an xparam-like trait that subtracts from a targets parry rate during an attack. It can be added to classes, states, weapons, armor, and enemies via note tags. Multiple sources of this trait stack additively. Every 1% of expertise reduces the chance for your attack to be parried by 1%. This xparam can also be shown on the YEP_StatusMenuCore screen using the short code 'xpt' via the exparamfix plugin, or the dual wield's menu extension.
I also added Pierce Parry, which is an effect that can be put onto weapons, states, or enemies, and reduces the targets parry rate by a % of their total. This effect is calculated after expertise has been applied. If there are multiple sources of this trait, only the one with the highest magnitude is used. This trait can also be negative, causing the targets effective parry chance to increase by a %. Actors who are dual wielding weapons with this trait will only get the value from the weapon currently being swung, allowing specific weapons to break parries more easily.
I was unable to implement the ability to use the attackers parameters in the additional parry chance formula. This is because the additional parry chance formula is used to calculate parry chance at all times, not just during battle, so an attacker cannot be part of the formula, as one is not always present when the calculation is being done. However, the above two additions should more than make up for this.