I don't think Sage has an issue in the damage department, the issue i find on SGE is that it's nowhere near close the other 3 healers to supporting their team efficently without swapping your kardia around and losing your mind.

I feel like what would fix Sage would be to have Philosophia, just like in PVE, where the kardia effect gets amplified to the whole team. I feel like that's what sage needs on PvP as well.