But that's not what the class is supposed to be (hello level 50 and 60 job quests)!

WHM can sustain a group (with difficulty), but not as efficiently as SCH, and has a lot less utility as a whole than AST, and all it has to offer in return is 600 DPS? (which is less than CS'd SCH since pets have their own stats and can heal just as well as a WHM [and better dots with actual debuffs])