For what it's worth Noct AST is really not as good as Diurnal AST. It has its uses, if you main AST you should know when you should (or should not) play it. So, if you're in an alliance, there's a good chance, depending upon your co-healer that you won't end up in Noct AST. even in a 4 man, you may end up switching to diurnal, or even switching back and forth.

I think SCH is more challenging than AST under specific conditions - in general- if you die, SCH absolutely SUCKS. I'll let you find out why, really it's the healer that suffers the worst penalties.

I do think that in levelling dungeons, SCH really does force someone to be a proactive shield healer, you'll have the fairy to think about, which will actually help you heal- and Sage won't have that- so there would be an adjustment- but I expect the basic barrier concept would be very similar.