Maybe not a potency buff, but lowering its cast time to 1.5s would make it easier to Deploy. You can already do so much to enhance that one shield (Fey Illumination, Dissipation, Recitation, Protraction, even buffs from other jobs) to cover more damage than SGE can ever wish for.

But like others said, SCH is already the best healer in endgame content, so I don't think it needs any changes relative to current healer gameplay.