It's really not though.
When you have two healing spots to fill and of the three healers available one has no group/raid utility and the other two do. Why would you bring the one with no utility? WHM needed to get some sort of utility to give them comparable worth to SCH and AST. Healing potency means very little so long as the healer can meet the healing threshold required to pass the content, and ALL healers need to be able to meet that threshold for balance reasons (and they do). But once you meet that threshold, more healing on top of that doesn't help but group utility does. When one of those three healers doesn't bring any group utility, they don't get asked to come along or get asked to swap to a healer job that DOES bring something useful to the table.
WHM's situation is only made worse by the fact that a) stoneskin removed, b) Plenary Indulgence (the new lvl 70 skill) does absolutely NOTHING if you haven't been spamming enough cures to proc confession at least once on everyone, and c) FIVE skills were stripped from CNJ/WHM and moved to shared role actions whereas the other two healers lost one or two.
WHM offers significantly less to its groups that SCH and AST.