I am not sure if there are a lot of misconceptions at this point. Most PF farm or learning groups for anything I see at this point have AST listed as potential for the healer slots. Since I main SMN, I join a lot of A1/A2/Thordan clear parties when I see them to make sure I give my other jobs some run in viable content, and no one ever complains when I join on Astro. There is nothing now that cannot be beaten with any combo of the 2 healers, or even any of the same healer doubled up. And in terms of progression raiding, you will see some groups switching from WHM/SCH to AST/SCH in 3.2.

Overall, I'd say a it's a relatively accurate perception by the player base. Good enough for either main/off healer in PF content, and a fair swap for a WHM as the main healer in progression raiding. You won't see them taking the SCH slot though in the strongest groups, as it does perform nearly as well as SCH in the offhealer role. But I don't really view that is a misconception, SCH is just really strong and tailor made for that role.