But you could as easily have it get most of its value from rDPS from supporting actions and still leave it as a damage-dealer... because it ultimately would be -- just a damage-dealer the majority of whose rDPS comes from buffing.
The only difference from swapping its label is that upon declaring it a separate role, (A) we are basically barred from giving any other DPS anywhere close to its level of utility without likewise rebranding it and (B) we are obliged to always bring a support now that it's a separate role that's separately matched (which in turn exacerbates its issue in greatly varying value between light parties and full parties).
Given that it's still ultimately rDPS contribution and the backbone of the job to fill with will still almost certainly be direct damage-dealing (else it'd be even less able to solo content than a healer would be)... I don't see the point in rebranding whatever jobs you want to add further support (options) to; just... add the support functionality and that's all that's necessary.
And do they have anywhere close to the healing output available to actual healers?Having distinct roles doesn't mean there's no overlap allowed. I mean, CLEARLY there isn't such a prohibition now. PLD and RDM have heals.
If a healer can get by on without MP and only a fifth of their kit, that's a separate issue. But even a single Medica II is, given the Maim and Mend trait, effectively 1300 AoE cure-potency; that's more than a Clemency to each ally. And they've more than enough oGCD potency to be unlikely to even need to spend the GCD.
Or, look at the difference in defensives available between a tank and a non-tank.
Now, imagine that level of distinction in support capacity between a "Support" and anyone else.
And what of a Support that has higher tanking capacity among Supports? Of a Support that has higher healing capacity among Supports? Do we then define the Supports as Support-Tank, Support-Heal, and Support-DPS?
Again, I just don't see the advantage over leaving support as a spectrum that any role may dip into to whatever degree seems fitting to the given job, especially since the only way to uniquely leverage it mechanically as its own role is to make its exact tools obligatory, which would then require homogeneity across the role. If left optional, we'd see just as much use from simply leaving DPS, Healers, and Tanks alike capable of support to whatever degree befits their job.