YES god i miss it lol 2 ast was pretty busted as much as a sch deployed shield good times!!!.
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Neutral Sect does compound with the shields of sch and sge but I think of it like niche like how warrior, paladin, etc compound because ast neutal sect shielding capabilities isn't as powerful and the shield timing might make applying one or two shields feasible but as you are on a timer rather than continuous it faces problems there. (It is also on a long cooldown for good reasons)
Even sge has a shields(s) that can stack with sch: holos shield (a shield that generates in addition to regen) and panhaima, haima (unless you choose to ignore those skills then everything is off the table).
Ast used to be able to replace sch shields though with nocturnal sect but that was the past...the identity of ast then was a flex healer either doing shields or providing big heals in whichever stance you were in.