AST aspected benefic has a 200 potency initial heal portion.
WHM regen does not. Seems like you forgotten that?
The potency of diurnal aspected benefic is actually 220 initial, 154 per tick after sect bonus. It does one less tick than regen, but the initial heal more than makes up for it, and AST has the option of using time dialation + celestial opposition every once in a while to increase duration.
Exiled_Tonberry was actually right to say that AST regen is stepping on WHM toes in the regen department. It's close when it comes to medica 2 vs diurnal aspected helios, but AST's regen equivalent is just better than WHM's for the added use of being a passable upfront heal, on top of already beating its total potency, and still having the option to extend its duration.
Don't like to have to do this 'pick apart'-thing, but it just keeps coming.
SCH's regen is tied to one fairy, has a 21 second effect with a minute cooldown, and overheals alot. Most of the time in full parties, people don't just wait to let the HOT do the work, which is why things like medica2, and diurnal aspected helios tend to overheal.
If you're counting the fairy embrace heal as a sort of regen, it's there to alleviate the fact SCH doesn't have benefic 2/Cure 2. Mind you, it has been nerfed every expansion release, and it's healing potency is lower than the displayed 250 would have you believe since it's a pet.
Really? A 2 min CD is an excuse?
It increases each player's magic defense stat on their character sheet by 20% of what it was, and that's the only free mitigation buff Eos gives, which is almost the equivalent of putting on another set of magically-resistant pants. Again, another 2min CD. AST has the option of setting up the bole if you're desperate for mitigation, which would likely be more effective than Fey Covenant anyway.
All of this isn't convincing me that AST's shields are entitled to have a cheaper MP cost, and no cast time in the case nocturnal sect's aspected benefic's on top of superior shielding all the time in nocturnal sect. You're not making a very good case.