"Gain a barrier with health equal to 20% of any heals you receive"
This is broken because of the following
This works in downstate, meaning that the barrier is multiplied based on how many people are ressing you. So technically it's going to be near impossible to dps out a target that has this rune equipped.
This also works with Signet Of Mercy, meaning that if a downed target gets ressed with Rune Of Sanc they literally get max barrier.
So it's needless to say that this is a huge oversight and needs to be tuned accordingly. And the only way to make it happen is by making this public knowledge. Enjoy it while you can I guess.