I'm sorry for not reposting dozens of ideas that I've contributed in the tank forum.

Parry will never be used until it either mitigates a large amount at a high rate or it contributes to DPS.

If it contributes to DPS then SE will lower DPS elsewhere.

So the answer to parry would be to start it in the 40% range and let it scale up. Parry stat increasing both rate and amount. They could also make it an extra stat on tank gear like acc was on 2.x healer gear. Or they could add slit tank gear into two groups.

Low def with crit/det and high def with parry.