Tenacity isn't even really a progression stat. Its benefits are too weak to be meaningful. Blind prog week 1 wipes are generally not understanding or correctly solving mechanics, and in Eden's Promise are typically due to non-tank players being dead since raid damage is much higher than in previous tiers. The benefits of a full Tenacity meld are too minuscule to really have a meaningful impact; you might as well use a typical BiS meld so you get that bit more of extra DPS so you can meet those actually quite challenging week 1 DPS checks on floors 3 and 4.

I think if they removed the DPS component entirely and doubled or even tripled its defensive benefits, Tenacity would be valuable and useful as a proper progression stat. You could achieve meaningful damage reduction and healing increase by stacking enough of it, which would take a little bit of pressure off healers during week 1/2 prog. But as it is right now, it's trying to do everything and it does everything poorly.