Tanks being crittable in general is a really terrible game mechanic, and parry should not be the way to resolve that.

Turn Awareness into another tanking CD, and make tanks automatically not crittable in tanking stance (if you are worried about pvp simply make tanking stance reduce crit chance by 10-20%, make npcs have a set 10-20% chance to crit, or simply make the crit reduction only against npcs), make autoattacks more significant, and faster, and you will end up with a model that puts much higher emphasis on total mitigation instead of spike mitigation, giving healers and tanks more say in how much damage intake there is, and making parry and vitality more attractive while maintaining the main tank in tanking stance.

Also would make PLD more attractive, making their "defensive focus" actually relevant in terms of total sustained mitigation that actively allows for higher healer dps.