I played nerfed SCH at the start of 4.0. I could not get past the fact that so many casual healers were never going to play SCH again. That was back when WHM and AST were considered meta healers. SCH's healing per second was so low and their MP economy was so small, and the pet AI was sluggish and nonsensical as usual. The problem with nerfing so hard is that players will drop the job and never play it again.

You almost never need WHM's healing potential in a coordinated group with how the damage patterns are designed in this game. The only fight this expansion where WHM's HPS was lucrative is UCoB for progression, although AST is fine in the right group. If they were to give WHM a 2-minute CD Haste buff for the entire party, it would put WHM in a better position even if only psychologically.