This is the questions that most raid group has to answer:

1. Can we bring AST to replace our normal WHM + SCH? AST can replace WHM right? --- Uhm no, it heals worst than WHM, has worse MP recovery, slightly worse DPS, and will force the SCH to be able to DPS less....
2. Can we bring AST to replace our SCH? -- Uhm no, it cannot DPS better than SCH, the buffs are worse than what the fairy can do because it is random, it does not have MP recovery as good as SCH, and the shield are far worse than SCH....
3. Ok, can we bring AST to provide buffs as good as bard or machinist? --- Uhm HELL NO!, the job can't even heal proper compared to the other two jobs, let alone giving the party meaningful buffs. You want buffs, you bring Bard or Machinist.