They can easily design the parry stat to work like the crit stat. Having the rating effect both occurrence and potency. This way parry tanks will have their parries stick out!

For example make like base parry 20% mitigation and and 10% base occurrence then have it climb to a max of 35% mit and 25-30% occurrence base on max parry stat. For a passive ability 8.8-10.5% mitigation is a full time Rage of Halone and definitely noticeable IF they raise the avg dmg tanks eat or lower the total HPS heals dish out (along with all the nerfs I suggested). Imagine using dark dance with max parry stat( better than bulwark !!)