I think it's more as deep as FFXIV got tangled in its healing mechanics. That started with "main heal" and "off heal" let's say. That Mitigation part of healing is well handled, and so it did not need to change so much with time, so the new abilities for SCH could focus on DPS, raid utility and a bit of quality of life. That's why it works so well, it fits the deal perfectly.
The problem is that Noct AST does not do as much is terms of mitigation, but still helps with buff. If only we could have that as main heal... wait, we can !

For me AST and SCH are very well balanced now, they are built on the concept that healers do more than healing, and they are designed that way.
WHM still falls behind for the numerous reasons we already know. It would be a shame to ruin one or two well designed classes because the third one has been left behind, as of course it's easier to nerf than buff and balance...