AST should have one default and one toggled sect

[Rilifane]

Synastry and Horoscope don't "force" you into anything.
Horoscope is a nice free aoe heal without charging it and Synastry is a sort of support tool IF you know oGCDs aren't cutting it anymore. Astro currently has the highest rDPS with a good chunk of it coming from buffs. They lose far less dps than a SCH or WHM while getting a ton of value out of a single hardcast. What more could you want, really?
Temperance and Asylum also increase healing done by GCD heals but nobody forces a WHM to GCD heal when those buffs are up. Same with SCH Fey Illumination. It's an added bonus in case you DO have to hardcast.
Neutral is the only skill that kind of "forces" you to GCD heal and with AST having the highest rDPS plus insane oGCD heal potential it's only fair that there's a tiny tradeoff tied to it because it's the only one they have.
Lilies are a always net dps loss over Glare even with Misery (unless you dump at least one during transition). Any oGCD from SCH is a dps loss unless solely used during dot refresh or Ruin II's 2nd weaving slot after having it used for ED anyway.
AST gets a free weaving slot with every single Malefic and that's way more than they need for cards. The rest of the time they're free to do whatever they want with it. So talking about "getting punished" as AST is rich. It's by far the least punished healer for using a GCD heal.
It's every healer's challenge to minimize GCD heal; take that away and you don't have to think about anything when it comes to optimizing. So removing the GCD cost from spammable heals would imo be a terrible idea.

Nocturnal is a nice choice for prog as it serves as a safety net if your party isn't yet sure how much they need to mitigate at which points. Regens not stacking WHM regens would largely be inconsequential. You neither spam Regen/ Asp. Benefic nor MedII/ Asp. Helios. And the only time when it's unavoidable to hardcast is during Shiva add phase and the party is split anyway.
Even for cases like back to back aoes during e7 tornardo it's easy enough to take turns with your aoe heals because both using them is overkill anyway. Diurnal would still win. Diurnal wins because it gets higher value out of every single oGCD and GCD and "unlimited" shields on demand are not neccessary. That the regens stack is nice for inexperienced healers but completely irrelevant once you get better.