so apparently Sage dealing a raid wide Aoe to his group is working as intended

[ty_taurus]

real gameplay example:
Pandaemonium 3rd Circle.

I (Scholar) get matched with a Sage. Before the Fight starts I cast my usual buffed combination of "Protraction" + "Fey Illumination" + "Recitation" + "Adloquium" + "Deployment Tactics".
Sage immediately casts E.Prognosis afterwards, reducing shields of everyone, requiring earlier and more heals, wasting more oGCDs (next to the 60s, 2x 90s and 120s oGCDs wasted already) and reducing dmg output of both healers.

Phoinix readys a raid wide AoE, I again cast my "Protraction" + "Fey Illumination" + "Recitation" + "Adloquium" + "Deployment Tactics" to shield the group. Sage again overcasts it by E.Prognosis.
I now wasted 4 oGCDs again and have to top up the group as instead of the shield eating the dmg, they got "HP-DMG" which needs to be healed (and the Sage dealt "Shield-DMG" to the group, by reducing the shield to a fraction)

This happened throughout the whole fight on every occasion.

Have you by chance thought to talk with your cohealer when pairing with a Sage? I won't say you haven't, but I feel like if you just communicate with your cohealer in a raid, even a short message when you enter the fight--something like "Hey, <name>, can you let me handle raidwide barriers since our barriers don't stack?"

Quite literally any problems that SCH/SGE could possibly encounter together could just be resolved through a little bit of player communication, and the benefits both jobs offer should drastically outweigh the entirely avoidable negatives.

And as others have put, SCH/SGE is an incredibly powerful duo. I've been progging savage as a Sage (I've gotten up to A3S at the moment), and I have to say, I probably feel the most comfortable with a SCH who's access to Expedient, equally prominent mitigation tools, and colossal barriers have been making healing feel a lot smoother than even AST. Not that AST is in any way lacking in its ability, especially with Macrocosmos that can just undo nasty raidwides, but with a SCH, party HP just doesn't drop like it does when I'm partnered with an AST or WHM.