AST doesn't need to be as strong as WHM/SCH. If it was as strong as WHM or as SCH, it would replace both jobs. Also, don't forget that the so called healing cooldowns SCH has are only ways to fill the gap between SCH and WHM/AST. Emergency Tactics transforms Succor in a 300 potency spell, like Medica/Helios, and Adlo in a 600 potency spell, weaker than Cure II/Benefic II. The stats are not the same when applied to the fairy, so the 300 potency heal they do is only 200, similar to Regen and Aspected Benefic (190 potency + 100 regen ticks); with rouse, that fills the gap and allows the fairy to do the same as two regen ticks or one use of Aspected Benefic. Indomitability also uses an Aetherflow stack, which means one less Lustrate or Sacred Soil.