See, that's why I think the split is a silly idea. If you want two healers to deal with 'Pure Healing' (or, bulk HP restoration in hard hitting scenarios like Harrowing Hell) and two to deal with mitigation/applying barriers (ie reducing the damage dealt by the hits of Harrowing Hell) then the end result of following that idea to its logical conclusion is that the two healers that do Pure Healing don't care about mitigation, and the two healers that do Mitigation/Barrier stuff don't care about Pure Healing. Effectively, all that this does is lock out the healers from interacting with the opposite side of 'healing design'.

As an example, WHM cannot mitigate things outside of Temperance. Why? WHM in older games has Protect, and in some games (eg 10) Nul-Element spells that protect the party from certain elemental magic damage. It's okay to take a design position of 'WHM is not as good as other healers at mitigating damage, but is incredible at healing after the damage is dealt', but by preventing it from, for example, using Lilies to apply raidwide shields, it just can't interact with any Barrier related mechanics. That then follows into 'we cannot have something that functions as a Barrier Check of sorts (eg Photon in A11S/TEA, Vulcan Burst in Ifrit EX/UWU, etc) in 4man content, because we can't guarantee that the DF will provide a healer that has accessible Barriers'. It just hampers content design, for very little gain. Especially considering that Barrier Healers can do Pure Healing to an extent, because of things like 'Recitation Indom', or 'Zoe Pneuma', or the stupid Regen effects on Sacred Soil/Kerachole that are so strong, they actually powercreep Indom and Ixochole

It's not like WHM should suddenly be the best at mitigation, either. I just think it'd allow for much more freedom of design for content, if WHM was able to apply Barriers (that are slightly weaker than SCH/SGE), via Lilies. If SCH can Pure Heal because of Aetherflow, or SGE via Addersgall, Physis, Holos (it heals too), Zoe-Pneuma, then WHM should be allowed to apply a Barrier via Lilies. It'd also mean that, when we need to prep Misery, we can get some value out of the Lily being spent even if the party is at full HP. And, it'd synergize with Plenary Indulgence, since, if the Barrier application doesn't have a heal attached (eg it's just a flat 250p shield, compared to SCH/SGE's 320p plus heal), then there's less chance that BarrierLily + Plenary would overheal