Yeah I agree that AST is is rewarded more for worse play in terms of damage. However I think that bad play is also punished more on AST because it makes your cohealer miserable. As an average AST will force you to heal more due to improper Star, CU, ED uses where as WHM there's not much that really punishes their cohealer (aside from the obvious of just not healing lmao). Can't tell you how many times i've been in a party with an AST who uses 2 Earthly Stars in a 10 minute fight and no CU or pops their Star when everyone is full HP. I would much rather have a WHM coheal than an AST coheal in PF for that one reason haha.
I've also been a huge advocate of nerfing Healer DPS in some way. In most groups our rDPS on healer beats most tanks which is ridiculous. I'm not sure how I feel about nerfing raid utility though because that's one of the things that keeps things interesting (looking at ARR where there was virtually no raid utility so there was no real coordination between players)
One of the biggest reasons for that is because people aren't really optimizing Ultimate aside from a few groups because it's a huge time investment and because of that WHM exceeds as they don't really have to do too much optimization to hit high at the highest level compared to AST. (I also don't think the gap between WHM and AST is as big as Alphascape leaderboards are making it out to be. If you were to look at Sigmascape parses were a lot closer and it's not like that gap increases overnight. Hell the #1 Chaos for WHM is in a pug lol.)
There's a threshold on speed affecting your damage in UWU as well because of kill time. Depending on how fast you kill the primals the more your CDs can get misaligned. I think at about 7:25? If you kill Titan any earlier than that you lose a set of 3 minutes as they won't be back up for Ultima. To compare our fastest kill time is 14:23 (14:20 if someone lbed at the end xd) and we kill Titan at 7:00 and lost a use of Litany/Voice where as a groups with a kill time of 14:50+ got that use. You can also gain an extra use of Potions if you pop them during Ifrit dashes but again if you kill too fast they won't be back up in time for the opener so you're knocked down a use there as well.
Another problem with killing Ultima itself fast is that it's one of those fights where the longer it lives the more DPS you will do. There's two reasons 1. You have more time to bring your DPS up after the massive amount of downtime and healing and 2. Killing faster can mess with your reopener. In my best we killed it mid burst and thats starting as soon as it starts gathering aether. If the fight would have lasted 30 seconds longer my PB could have been around 100 DPS higher.
I'm not saying that's the reason that WHM is higher because the amount of groups actually killing it that fast is small but just comparing the top healer combined between SCH+AST and SCH+WHM and the WHM did 20 more healer GCDs than my AST. And ours isnt even completely optimized. Our current map out for heals is based around Selene where as the SCH+WHM one isn't. So that's 20+ healer GCDs less with Selene. Whispering Dawn is all fluff healing in with out current setup because Earthly Star covers all of the damage Whispering would. Sucks that we weren't able to get a kill with it because of Alphascape releasing. Anyways the only reason Selene is possible is because Earthly Star basically covers for WD and I can't imagine a WHM being able to do that without too much of a loss.
The pDPS discrepancy between WHM and AST is definitely over exaggerated though. It just comes down to the point I made before and that there are no truly great groups running with WHMs compared to their AST counterpart. Sure you can optimize on WHM but that's only a piece of the puzzle. The other halves being kill time, buff alignment and coordination and just looking at the top parses in Alphascape for WHM they are very mediocre in those aspects. Like I said earlier it's not like the DPS gap between WHM and other healers can just magically grow overnight. The best WHM in O9 was in a pug and is currently ranked #5 across all healers for that fight.