Remember that when SB dropped SCH suffered from quite a few issues, and since then they've been given constant adjustments and buffs to bring them up to an acceptable pick. AST had also had several changes throughout the patches, but the only problem we have is that WHM has barely been touched. So yeah it's great to help the other healers as they did actually need it, but WHM was left dead in the tracks.

Give WHM more attention and readjust/fix several things and we won't need to nerf the other healers at all. Chances are though, at this rate it'll be the next expac before WHM gets amended.