If Red Mage were in FFXIV ARR... It would be like this!

[Alise]

Think about current hard end-game check point.

Okay, during the coil progression (before beat it first time). many of the cases were hard DPS check that even if a pure dps class were to be distract, die, slow down, then party would wipe. So if you replace your DPS with RDM, then wipe due to not enough DPS.

Then here come another healer check. It come as place to place where it require stoneskin and aldo +> spam cure-II, specifically in other to survive certain attack. So if you replace healer with RDM, then wipe, because RDM can't give big heal. (and they shouldn't be able to).

Then there are place where Tank need to swap between 1 and 2. If RDM fill up tank spot, then it is also a wipe.

All in all, the battle design isn't kind enough to actually have a class that do no good at anything.
If it gonna be the best debuff class or buff class, then it may have its place, but that mean SE will need to reduce their DPS check, or heal check, or stop tank swap to open up the spot to let a balance job join. Basically, if they want battle to be flexible to any class, the hard-check will need to be soften, and that mean people with pure class gonna get it pass check point easy. Therefore, to keep content hard, the design of content would need to match role specialize. If RDM doesn't specialize anything then it doesn't fit. Sure it could get specialize on buff or debuff, but that isn't what players base ask for right?

Particularly, this is why most players stop using RDM on end-game of FF3, FF5, FFD. Only class that is best on something is viable in real end-game. And it was why RDM in FF11 was design to be Refresh class. cuz it is good at nothing else!