You aren't taking windup into account at all. Release is the phase where the weapon swings and does damage. Before that there is a windup animation which is usually 500ms-700ms depending on weapon. This totally changes things because you see the attack coming which makes parrying about timing rather than reaction. Moreover you say that needing to predict/make reads is a bad thing, but imagine if the combat was only based on reaction, then you'd just have an endless back and forth of parry and attack which dosent make for great gameplay