I've done it on the main tank only so I can focus my attention elsewhere. That's it. I agree that in an ideal scenario, you wouldn't even use anything but the fairy to heal the main tank. That's not what happens though.
There are situations like Akh Morn on O8S where the party takes a bunch of AoE and you don't necessarily want the main tank to turn the boss to get them in there. I'm aware of the 'Stand in the Cure III/Star or you're fucked' situations. Hell some of the movement I do on SMN is a compromise between what makes the healers' lives easier and what helps me see the fight better. There are spots in Kefka and O7S where the tanks and DPS would be split up but may require a minor HoT prepared beforehand just to minimize time spent healing them in order to focus on something else more important, like mines and adds, or Kefka clones. Those are the situations I'm referring to. Not the BLM who doesn't want to move whatsoever. Though we have one of those, too.
For high mobility high healing situations WHM has to plan their few AoE cooldowns in advance for the most part. I've seen ours pre-pop Asylum where they want people to wind up just to keep it rolling on the tank for a few ticks in the meantime, tack Regen (not Medica II) on players they won't be able to reach for significant periods of time to deal with positioning requirements for mechanics even if the first two ticks were useless, Cure III bomb others they can reach that naturally stack up together and set up PI in the process, and hold Assize for that exact moment where players can collapse in to get that extra safety top off even if it meant losing a use or two over the fight as a whole in prog. It was basically required to use all of those at specific points for Forsaken on them if they wanted to hold up Swiftcast for raises. Which they did.
I'm aware that AoE hots aren't worth stacking up generally speaking. The single target ones, however, are in some situations. Lengthy multi-hit busters are a thing. A lot of the HoT based AoE cooldowns actually can handle back to back AoE they have no business handling with maybe a single medica-level AoE heal added in at the right time.
Where did I say Noct was spamming shields specifically to make up for the loss of their HoTs? I said they would spend more GCDs, yes, but that does not imply they'll only use Noct Benefic to do so. They would top off a tank via Benefic I/II where possible, not those. You're clearly assuming I don't know what the spells do. The only reason you'd ever use a Noct Shield that way in that degree is if the tank was dipping below half HP, you knew you had to move, and knew it wouldn't lead to overhealing when you could heal them with a Benefic I/II later because the autos would break the shield in time. This kind of situation happens when the other healer isn't doing their job, yes, but it also happens when the tank's trying to get damage in too. Sometimes you just want the tank to be at a comfortable HP level until the actual problem mechanic happens and double regen does that for you with no extra effort on your part.
Whether it's a WHM not using a regen or a SCH AFK spamming Broil II or a Tank sitting in Shield Oath, things happen. Dutyfinder pugs is not the place to look for others to rely on. SE has a tendency to make sure all healers have what they need to handle that content and not give a damn beyond that.
WHM's problems higher level content are the fault of SE being unwilling to give them ways to work around them, but I'd want them to do it in a way catered to WHM's current strengths. I'd be just as happy to see WHM get more non-shield mitigation, like their own version of Fey Covenant. They deserve to have access to better healing cooldowns through stronger Lily effects and better forms of generation. If they must get a shield cooldown, there are ways to go about it that still fit WHM's pure healer niche, such as giving them Divine Seal back with an additional effect cooldown that lets them specifically overcap people's HP temporarily, or making Divine Benison AoE but restricting that ability to a specific Lily count. SE's claim that they're the 'basic' healer is why it's in the spot it is at the moment.
I don't have a problem with Healer homogenization, so long as the way that's individually accomplished is interesting. AST gets stance swapping. SCH gets the fairy and Aetherflow. WHM gets Lilies. SE doesn't want to change up fights enough to make some healers clearly better, but does like to cater to the problems of certain classes over others, which is what resulted in this healer disparity issue happening two expansions in a row. Pretending that AST doesn't need some of the tools SCH already has to make it better with WHM specifically because 'it has better shields' is flat out untrue. The same way that it's untrue to say WHM is good because it has the best mana management and AoE Healing cause Thin Air and Cure III are so strong.
Neither is correct or practical in practice.
AST needs limited sect swapping. WHM needs love.