I only have Conj to lvl 15 so I cannot speak to the whole breadth of the healing classes. With Scholar and AST both at level 60, I feel the AST has enough strengths to be viable. From my own experiences, Scholar has better global cool-down ability with their pet picking up heals, a much stronger mana refresh ability, and better single target dps. Placing your faerie in boss fights really makes a difference, and overall, the class allows you to pull through some would be wipe situations. The strengths of the AST is it has greater access to the stronger heals, you can spam your 680 heal and both of your aoe heals if need be without waiting for cool-downs. AST is also a lot more mobile than Scholar, I can run around quite a bit and still not worry much. I think that overall Scholar is the better class to bring into a fight for healing, and that AST functions better as Diurnal Sect with a Scholar versus going Noc with a WHM or fellow AST.