I did Ultimate with AST (1%) and WHM (clear), and I can say it's far more easier to do this type of fight with WHM than with AST.
Why ?
- AST require more mental load because of : the cards system (you need to know perfectly how to deal quickly with cards depending of the situation), plan Earthly Star 10-20 (or 30 sec with CO) in advance. More cast per minute (mental load).
- Mana management : if it's not managed well or too much death, you can't continu the fight.
- Healing must be accurate, efficient and well planned. Cure III or Benediction is not here to save him and the group in emergency.
With the recents changes to AST, the real benefit he will have now is his mobility, that's all.

So, I don't see again the problem. WHM is similar to RDM, more safety to the group. If you are not for that, change your job.
If you fear WHM will disappear of the screen, it won't.