Idea: Split Archer into Bard and Ranger

[Duelle]

At this point though, WHM would require Geomancer to strip away nearly all its dps abilities, and all three would likely be scratching their heads wondering why they only have significantly fewer abilities than every other job in the game. ...Would have to nuke AST dps too...

Not necessarily. ACN happens to be built around DPS, so making the transition to healer would require certain abilities changing to better-fit that role via the SCH crystal. Conversely, CNJ is built as a healing class, so the GEO crystal would likely change Cure, Cure II and Cure III into Water I, II and III. GEO would get Aero III and Stone III, and could be designed around a natural flow between water, air and earth (headcannon would call this the "Geomancer's Parable"). The wrench in the gearworks would be, incidentally, Cleric Stance.

I'm all for making SCH more different from its counterpart, but stripping away SCH dps to make an already high-control healer even better tooled in its healing does not sound like the solution. (Admittedly even the loss of Bio I and Bio II would not 'utterly condemn' SCH dps outside of raid settings, and their further improved control may then make them the dedicated main healer -- but that kind of re-balance would then need to be made on every healer job, not just the dual-job SCH.)

Correct on both accounts. SCH would still have Ruin I/II and Miasma I/II from its parent class. And who's to say the job abilities (remember that Sacred Soil is no longer a lv50 job skill but a skill you'd gain from learning Shadow Flare) wouldn't include maybe 1 DPS skill? Broil would have been a good candidate to replace Sacred Soil as the lv50 quest reward.

It won't change that if you want their to be any variance in damage taken rates there will be downtime during which dedicated healing output is mostly wasted. I like being able to contribute during periods of less intensive healing.

You still would. Your DPS relative to the DPS would just be less.

The intent is not to kill off SCH DPS, but to reduce it while also making the job crystals bring about a bigger change to gameplay. This way one job crystal becomes a sort of extension to the parent class, while the other changes aspects of the parent class to become its own thing. I admit it's easier to do this with caster jobs than it is to do with melee since you can recycle casting animations. Melee jobs would likely require brand new animations and more.

And with healer off-role participation being so demolished, tanks would probably use tank stance even more sparingly.

Not if you were to tie enmity and survivability directly to the tank stance and adjust post-30 scaling to make it required to stay in tank stance to hold the mob and live through its attacks. Note: this would require some ability reshuffling, such as making PLD get Shield Oath at lv30.