Genuine question:
Are we talking about Savage content or normal Dungeons?
If we're talking about normal dungeons, then the healing requirement could be doubled and still be doable with Medica 2 spam. So that wouldn't hurt the casual healer at all.
If we're talking about Savage content, then the DPS contribution isn't optional.
So no, you can't use this deflection.
(That is, if we're talking casual content, then increasing EITHER is in the same boat of not mattering, so that doesn't support increasing damage and not healing; if we're talking hardcore content, then increasing EITHER is in the same both of very much mattering, so that doesn't support increasing damage and not healing, either.)
Yes, it would basically have to be negligible. But as we've said when we've gone over this the hundreds of times before, "more work" has to be rewarded otherwise it is unacceptable to the very people demanding "more work".
Healing requirement, in a VERY technical sense, is a sliding scale from 0% needed healing to 99.99% of health damage provided damage waves have enough spacing to get people back up to 100%. More than that if we include mitigation, but we're just talking about healing.
Damage is also a sliding scale, but also has a lower bound of "fails Enrage", and the more difficult it is to access damage, the more difficult it is to clear Enrage.
I feel like this is is the point of contention and people aren't quite getting it.
IF the damage output is different, it isn't an "option" anymore. It's only an option when it's functionally identical. No one wants a Stone-Aero-Water rotation that does the same exact damage and effects as a Glare-Glare-Glare rotation, but that's the only thing that would be absolutely optional.
This whole thing is why I pitch the 4 Healers Model idea all the time, since it addresses this by letting players who want to have to press more DPS buttons to pick the hhealer Job(s) that have them, and those who do not want to press them to choose the healer Job(s) that do not.
You're lumping a bunch of people in a group and saying they all suck. "You can't upkeep Dia? Well, obviously you wouldn't be able to cast Cure 2," which is a nonsensical argument. "They can't handle more DPS buttons because..." NO! It's because they don't have a mind for (or any interest/fun factor from) DPS, not because they don't have "awareness" or "oversight".
Look at all the DPS players in the game who can handle complex DPS rotations and clear high end content so clearly have awareness and such, but you throw them on a healer and they freak out and can't do it. It turns out, "awareness" to healer health bars and "awareness" to DPS CDs aren't identical skills.
You really seem to have a problem grasping this concept and I have no idea why. What you're doing is essentially saying anyone bad at playing piano will also be bad at harmonica and sculpting, but anyone good at piano is also able to play literally any instrument on the planet or perform any kind of art that exists with equal proficiency.
There are TONS of people that fail at DPSing but not at healing and mechanics. There are TONS of people that fail at healing but not DPSing and mechanics. This view is not only insulting, it's outright wrong.
To be fair, you have no way of knowing those aren't the "Green DPS healers", not the Sylphies. If healing became literally Medica 2 spam, the "Sylphies" would be the only ones that would do it.
Yeah, this is the ultimate problem. But I continue to contend this is due to the oGCDs. Healing needs a total top-down revamp. As much as some people like "healing plans", those are as detrimental to good design as the 2 min meta is. Both hamstring design.
Think about it, we don't have MP management because of powerful oGCDs. We don't have breakup in the Nukespam because of the oGCDs. And "weaving" probably wasn't even some high minded design objective so much as an accident between janky netcode and workarounds for responsiveness. It's influenced the expectations for healing and has limited how "healchecks" can work since oGCDs provide so much healing that it generates the Roe/Sebazy/etc noted problem of how high healing demands would need to be to actually stress the healer kits.
At the core, the oGCD healing model is a pretty massive problem, and any solution has to at least acknowledge that being part of the issue.