We've probably got so much little things adding up to the healers not needing to heal very much that we probably need the newer encounter damage to increase to "fix" the issue first. Forsaken Roe's Aetherblight idea does look good as one to add. It also gives us a reason to consider Esuna and could open up an AoE Esunaga niche for a healer too. More than likely, SGE could probably get that one.

As for the WHM discussion, I do agree they have a niche for immediate and strong reactive heals. Although I do believe Supersnow with him essentially saying this niche isn't being used enough for current encounters. Another reason to consider that Aetherblight idea as well as more of those 1HP White Holes?

If Temperance isn't enough mitigation, the Protect and Stoneskin spells could be considered for more Afflatus heals as Forsaken Roe suggested too. It could also be possible to consider if a WHM cooldown could use a SCH Protraction-like effect. That way, it feeds into the big heals fantasy while also allowing the raid to survive the major damaging AoE mech.

I believe Snow also mentioned an HP sharing cooldown as another secondary cooldown for a healer to possibly get (SGE maybe?). I can confirm this works well for Shamans in WoW and this makes the off tank HP more useful.