is AST a better substitute for WHM or SCH?

[Cynfael]

While it does compliment the SCH's inability(with Selene) or limited(With Eos) ability to provide regens, there is just two problems Diurnal has.

1) It does not affect Essential Dignity like Nocturnal does.

2) All of the AST's regens are laughably weak. So weak to the point it makes you think you never applied them in the first place, or at least you'll be healing like you never applied the regens. You need barriers to make them at all effective.

The 5% healing potency buff from Nocturnal doesn't make or break anything. It's true that Diurnal's 5% attack speed buff does nothing for abilities like Essential Dignity, but we would only care about these differences if both Sects were on roughly equal footing otherwise, which they unfortunately aren't.

AST regens are fine. The only way they really lose is if you compare the HoT from A. Benefic directly to the WHM spell Regen, as Akyio notes. We're still talking about a lot of additional healing potency over time, however. Discounting AST HoTs would be a mistake.