So I was trying to run a counterattack styled Sentinel and of course went for Rebuke. I noticed that it was dealing a pitiful amount of damage even if I took upwards of 10 hits from enemies during the duration.
I ended up just quick-using the skill and doing a full channel against some void worms. Both times, the worms lived with about 1/8 of their health. If a quick-use did 7/8, then surely after taking a couple hits, it should kill given the 20% more multiplier.
As such, I am under the impression that the built-in damage buff for the skill is not working properly