Another WHM chicken little sees the sky falling. The sky is an AST.

[Trunks]

My point in all this wall of text? Even if AST/SCH brings the most raid utility and DPS to the table out of all three healers - a fair number of groups still run WHM for the safety factor

That's a big assumption. Actually my garbo group of casual scrubs runs a WHM because I hate Astrologian and I can do just enough personal DPS to justify my existence (except when we get final bosses that spam near-one-shot mechanics because SE refuses to stop handing out shields and mitigation cooldowns like it's a bloody Oprah giveaway). WHM isn't optimal, but it's viable. I would bet that for most groups, running a WHM has nothing to do with the heal throughput (in fact that heal throughput is as much a curse as a blessing because when I put the group on my back and try to carry them to victory, I get aggro and die, because SE brilliantly designed a game where tanks are disincentivized from doing their one job); more likely it comes down to the personal preference of the player, because it's easier to compensate for any small deficiency in WHM than it is to find an entirely new healer. When those deficiencies stop being small and the raids are balanced around the assumption of comps that aren't awful, what do you think happens?

That's all out the window, and now I'm either gimping my group or playing something I hate.

Protip: don't obliterate your most popular healer job and one of the most iconic jobs in your franchise on a whim. They're slapping a bandaid onto AST. Except AST isn't bleeding. It has broken bones, and SE's the one that broke them with their SCH Sect / WHM Sect design.