I've not seen any real use for crit defense on my hunter. I just focus on my main stat, crit, vit and tact mit. In raid situations I keep my crit capped, somewhere around 39k mastery, and around 45% tact mit. I have one of the crafted necklaces with crit D on it, but rarely equip it. Except for the rare times I slot that necklace I run with literally 0 crit defense and have had no problems completing any of the t2 erebor raids.
Eilinel, Bejaren- 85 Hunters
Gerlendad- 85 Burg