Pros and Cons of each Healer Role

[VanilleFang]

Pros:
WHM: Cure III, Benediction, Assize, Most HoTs
AST: Cards, Disable, No cast Single-target Shield, Versatile
SCH: Fairy, Critlo, Deploy, Supervirus, Most DoTs, Most mobile, Versatile

Cons:
WHM: Not-so-versatile
AST: Least DoTs, Least Ohshit skills
SCH: Least HoTs

You forgot to include that WHM have the most AoE healing spells of the three (Assize, Asylum, Medica, Medica II, Cure III) as well as Stoneskin II. And buffs from cards can be seen as a positive as well as a negative because... You forgot to mention the RNG aspect of the Astro.