@Apeiron
Meanwhile a SCH+WHM combo can just use indomitability+assize and that's it (and you don't even need to waste MP in the process...in fact the WHM gets 10% of his MP back). Actually they can do a lot of different things with their amazing skills. Party topped, ready to dps or heal the tank. Notice that we're talking about raid progression here. Trivial encounters like extreme primals can be easily solo-healed by every healer if your party is good enough.
Now, allowing that the AST is smart enough not to override the SCH shielding
So you're saying an AST should not use 2 of the 5 healing skills he/she has access to. Why not just solo-heal the fight if that's the case? :P