While some of your ideas are decent, I don't think what you're suggesting balances AST with SCH well at all. I know you're a WHM first and foremost but your suggestions would merely allow AST to be super competitive with WHM. I also personally don't think that'd make AST all that unique either, they'd be a few steps closer to WHM that what they currently are. Now that's just me, and I don't think this is necessary bad but why make it even more of a clone by touching durations and potencies while in Diurnal only?

You're not suggesting anything to fix the bad interactions of Nocturnal skills with TD/CO, you don't touch on the mitigation perks SCH has over AST (Covenant/Deployment Tactics/CU having 3x the CD of Soil), you're not even touching on what is your main argument: AST can't DPS well because they can't stay in Cleric for a very long time. With your suggestions, they could DPS more while in Diurnal but still would have to heal just as much as they do now in Nocturnal. You're basically completely ignoring Nocturnal exists or implying it's good as is (which comes as really questionable for someone with such a raiding pedigree as yours), when Nocturnal is widely considered as inferior to Diurnal and to SCH in the first place.

I mean, let's be realistic here: this is how you get rid of WHM, not how you make all 3 combinations equally viable.