I think when it comes down to the AST/SCH compo, it must be easier on non-AOE healing fights. The AST/SCH should be the better compo in term of DPS (Selene + cards) but since most of the time you end-up using Eos with an AST.... Don't know.

On the other hand, the WHM/AST (diurnal) seems always better as long as you don't need the extra shields / the extra HP to survive. The raid AOE healing can be done by the WHM alone so AST can focus on tanks, some mechanics and dpsing. I think you would have killed it if one of you switched WHM, just the same way you switched SCH. I'm not saying it would have suddently started to be easier.

But still, I play both AST & WHM and something is very lacking. I don't need more potency heals, I don't need more MP (only using Ewer since others jobs won't need it most of the time), but I need more "oh shit" buttons and I need to feel like my cards are more useful. Each time your Royal Road a card, you basically aren't using any card for 30s, added to the 30s needed to draw the RR card, it's 1 min without any card rolling... Each time you already have a RR buff and you draw a card that you don't need, it's useless and you need to click it off. Each time you want to use RR AOE effect and even Celestial opposition, you know there're a lot of chance you won't hit ALL the raid so you're not using the max of your job but you can't do anything against it. Each time you use Collective unconscious in diurnal... You feel weird because you will NEVER stay still and use the full duration of it, so once again you're not using your spells at the maximum, and that's the main issue I see on AST.