Oh, when I refer SCH has better shields I mean they have better flexibility in shielding and potential shield values. For shielding values alone, AST and SCH shield values are in competitive range.
Yeah, looking at GCD AoE, potency wise Succor is worse. I do think SCH needs a buff in that regard. Thankfully the difference is that unlike AST, SCH has abilities to bolster their true potency value on their spells which are already fairly close in effective potency. I believe Nocturnal Asp. Benefic vs. Adlo is really a difference in job flavor - Adlo is weaker unless it crits and grants a double shield that it overpowers an AST asp. shield. Adlo is either a 375 potency shield or a 750 potency shield with a crit with 300 potency heal. With Fey illumination, Adlo becomes 412 potency/825 potency shield with crit and a 330 potency heal. With Dissipation, Adlo becomes 450 shield vs 900 shield with crit and a 360 potency heal. while AST's asp. benefic is a flat 500 that doesn't change with a 200 potency heal. If they gave more shield power to SCH, they would have to change the amount of raw healing done.
Don't forget Deployment Tactics too. Although it isn't as good as Celestial Opposition alone for raw mitigation or cd, if you pre-shield Adlo or Adlo before huge damage, SCH can spread that shield after in addition to Seraph's Consolation for more shield potency than succor. I do think Deployment tactics need a buff though, perhaps either lowering its cd and/or giving the Galvanized shield a boost even if it cannot extend Catalyze. Imo more ways to shield rather than dumping it all on one skill is much better as long as the shields aren't too weak.
That's not to say SCH isn't in a fairly terrible place right now and the fairy likes to ghost, but AST don't have as much shield flexibility than SCH - they have more survival power though thanks to being able to flop between regens and shields with their oGCDs. They do remain largely competitive with SCH though for that reason.