Do remember that Ephemeral Mending is BiS for Shadow Tanks, and by a HUGE margin. Changing that relic directly will have a big impact on shadow tanks gear and survivability.
While I agree in general with not shafting Sin/Shadow Tanks I still think this is a "HEALERS" Relic and needs to be correctly balanced as such. We have several defensive relics today for tanking class and not really any "HEALER ONLY" relics that are worthy of a mention. SA and BA do have several benefits, but not dedicated like several of the DPS Relics (Internal, Energy, etc.).