As the title says, I hate the split. It's not worked. SCH/SGE is a completely viable comp even for early progression, is often safer due to having more mitigations, and have enough burst healing between them to cover the lack of 'pure healer' output levels. By contrast, WHM AST barely functions as a comp, even in BIS when a fight is learned, due to the sheer amount of mitigation required, and the lack of mitigation between the two (CU once a minute, Temp once per 2min, Neutral Sect as the only source of AOE shielding)
To go along with the ancient thread I made like a year ago where I outlined a possible idea of a 'spectrum' of Pure vs Barrier, rather than the current 'you are a Pure, or you are a Barrier', recently I had an idea of sorts on how to accomplish such a thing. As outlined then, and again now, SCH/SGE is a valid comp. It can function in even the hardest content (and is sometimes the best choice). WHM/AST and SCH/SGE, in any combination of one Pure/one Barrier, functions as a valid comp, as it's the 'intended by developer' setup. The only problem comp is WHM/AST due to it's mit issue, and if that were rectified then the 'spectrum' paradigm would work
In that old thread, I outlined an idea for WHM where it would gain several new skills, including an actual DPS rotation of sorts, a new gauge to 'manage', and important to the topic of this thread, two new shielding Lily spenders, Afflatus Sanctuary and Bastion. With this, WHM would have the shielding half of 'Barrier Healer duty' covered. On the flipside, it has very little in the 'mitigation' department, with only Temperance.
So what if AST were to be the 'mitigator' in this situation?
All we would need is some new traits to change how some existing AST skills function, and AST could have the %mit side of Barrier healing down. This could be done either by adding the traits to the skills as they are (so the skill has it's current and new effect simultaneously) or by bringing back the old Diurnal/Nocturnal pre-pull choice. I'd personally vote for Nocturnal Sect, as it allows Neutral to justify it's existence, it doesn't screw up the old Sect lore, and it's just a nice thing to have, for the player to feel they have some 'agency'.
Example effects:
Collective Unconscious
Under Diurnal, applies it's regen for 15s, and mit for 5s, unless channelled.
Under Nocturnal, this could be reversed (as was the case in SHB), where the mit is 15s and the regen is 5s unless channelled. In SHB, the mit was also 20s
Earthly Star
Under Diurnal, heals for X, after 10s grows to the bigger star and heals for Y.
Under Nocturnal, applies 10% damage down to anyone standing in the star's field as it charges, but the star heals for less pure healing potency upon detonation (example numbers, 400p instead of the current small-star's 540p), and does not grow to 'big mode' (instead staying small, and detonating after 20 seconds)
Horoscope
Under Diurnal, provides a buff to allies that heals for 200p upon reactivation or expiration of the buff (10s duration). Using Helios or Asp.Helios empowers this buff, causing it to last an additional 30s, and heal for 400p when it's effect activates.
Under Nocturnal, the buff is replaced with 'grants 5% damage mitigation' while it is active, and causes no healing upon expiration. Helios/Asp.Helios would still be able to extend it's duration, meaning a 30s duration for this mitigation tool. It is for this reason that it is only 5% mitigation, instead of 10%
Celestial Opposition
Under Diurnal, heals for 200p, plus 500p over 15s as a regen.
Under Nocturnal, heals for 200p, plus applies a 5% damage mitigation effect for 15s.
ALT: heals for 200p, and applies a shield of 300p (would prefer the former, due to reasoning explained below)
With this, AST's only source of shields would be the single target Celestial Intersection, and Neutral Sect, leaving the 'shielding' part of the WHM AST comp almost entirely in the hands of the WHM. On the other hand, with only Temperance in their kit, WHM would be almost entirely reliant on the AST for the '% mitigation' side of Barrier healing. While playing with a SCH/SGE, the two would be able to just play as they do now, focusing on pure healing throughput and letting the SCH/SGE do mitigative things.
Additionally, if that is somehow not enough mitigation to work with, AST could even get Disable back