Why exactly do Galvanize and E. Diagnosis overwrite each other?

[Astronis]

Double shield stacking could allow for players to cheat the "dance" since many of the mechanic's debuffs are applied the moment they damage the player and a shield that covers the whole damage nullifies the application of those debuffs.

Virtually guaranteed it's this. If you can avoid the debuffs via shields, there's all manner of mechs you can cheat.

[noumen0nn]

It's a balance thing, like others have said. Shields are very powerful, hence why the majority of them are tied to long-cooldown abilities. Things like Divine Veil and Shake It Off can stack, because the merit of getting a super-powered shield is balanced by the cost of committing both resources at once and not having either available for the next 90 seconds.

If you could stack SCH and SGE's gcd shields, it would trivialize even the mitigation checks in ultimates, for the relatively low cost of one broil/dosis every time you do it.

Double shield stacking could allow for players to cheat the "dance" since many of the mechanic's debuffs are applied the moment they damage the player and a shield that covers the whole damage nullifies the application of those debuffs.

While this is true, there are more debuff-applying mechanics that don't work this way than ones that do, and the ones that do can already be cheesed by stacking other shields or using SCH's recitation-aldo-deploy. Still, to be fair, that also costs a resource, whereas with stackable gcd shields it wouldn't.

[VeyaAkemi]

I suspect, rather than balance reasons, it's mechanical. That functionally Adlo and E.Diag are the same thing with a different skin and so short of writing new code to differentiate the two abilities it's impossible to stack them. That would allow for legitimate accusations of laziness on the part of the dev team but they get enough of those as is.

Why would this be the case? we have a lot of objectively identical buffs that stack, it doesn't matter if there are 6 WHM in an Alliance Raid, all of them will be able to apply their own Aero/Dia DoT freely, or double Medica/Regen buffs, and those are completely identical, not just in functionality, unlike Adlo and E.Diag, so on, it's very clear that it's a balance choice which kinds of buffs do or don't stack.

[DiaDeem]

Because you shouldn't run double Shields on Savage, you evil creative gamer!!1
Now go wall-to-wall HM ARR reworked Dungeons with our streamlined horrible Trust system.

[Daeriion_Aeradiir]

Balance.

Double shield stacking could allow for players to cheat the "dance" since many of the mechanic's debuffs are applied the moment they damage the player and a shield that covers the whole damage nullifies the application of those debuffs.

It also increases the problem of double shield comp being far superior healing wise than shield + regen or double regen

Every single debuff in Savage+ these days always applies regardless of how much damage you take, they intentionally started doing this in EW when lots of vulns were being ignored in Eden tiers due to super shielding.
If any direct mechanic even remotely dangerous in any fight's "Dance" could be ignored with shielding, you 100% bet stacking tons of party mit on it to zero it out would become mandatory since SCH can save a crit-adlo for it, but that's not the case, all debuffs that matter get applied anyway.

That being said, it is the general correct thought process. The shields don't stack because most healing in higher end content comes from preventative measures rather than reactive healing, so double shields would be stupidly OP, especially in phases like TOP P6 that are entirely mit-check based rather than healing based. Double shield healer is already insanely strong even without stacking shields because of the extra mit, preventing shield stacking is basically the one thing that merits exploring AST/WHM as the other option.

[weebtext]

I suspect, rather than balance reasons, it's mechanical. That functionally Adlo and E.Diag are the same thing with a different skin and so short of writing new code to differentiate the two abilities it's impossible to stack them. That would allow for legitimate accusations of laziness on the part of the dev team but they get enough of those as is.

It is a shame though that the two shield healers conflict with one another, I would like if they changed it so that when a SCH/SGE applies a shield over an existing one it checks instead against the crit shield rather than the base one, that way at least it's semi-deconflicted.

The fact that even after all this time they still haven't made it so the bigger shield stays applied infuriates me. Nothing is more soul crushing than applying a mega-shield as SCH just for the SGE to obliterate it with a dinky baby shield, and the worst part is when I play SCH I end up paired with a SGE most of the time

[Kohashi]

Because you shouldn't run double Shields on Savage, you evil creative gamer!!1
Now go wall-to-wall HM ARR reworked Dungeons with our streamlined horrible Trust system.

pressing 1 or 2 buttons is now creativity, much wow, much amazement.

The funny thing is, double shielding in savage is actually a thing, however it requires some coordination.

[AmiableApkallu]

Fun thing I learned today: Differential Diagnosis and Catalyze do stack:



(Edit: Not the shields the OP was talking about, but it feels relevant, all the same. )

[Jamini]

Honestly, I just wish we could swap jobs within roles. If I'm queued as a SGE and my Co-healer is another SGE or SCH, I'd have no problem with swapping to WHM.

You're actually weakening your team by doing this. SGE+SCH is the strongest healer combo by far- and no serious raid healer GCDs unless you have downtime or your party dies without it.