[Post 3 of 3]

As others have said, Parry is in a really bad spot right now, and Vitality doesn't really help your healers (outside of giving them a wider margin of error). You get more mitigation from an enemy that is killed 2% more quickly because of boosted Tank DPS than you get from the Vit and Parry on your accessories (I believe it was calculated to be something like 1% less damage), and since Slaying and Fending accessories both have 1 Defense and 1 Magic Defense, it absolutely makes sense to suggest that tanks should use Slaying pieces in their accessories slots.

It also doesn't help matters that encounters now are tuned with high tank DPS in mind, but I digress.