Believe me when I say I'm with you in wanting an actual support role job. That was the primary reason I leveled BRD here (I was one of those BRDs in XI that I mentioned). I also share the same criticisms about the devs not being able to properly introduce the concept. You've already pointed out the BRD/MCH aspect, but also consider how they treated AST upon release. Gimping it just like they did BRD/MCH, seemingly under the premise that the RNG cards are so powerful that it warrants subpar primary role output. Clearly, they were wrong on the potency of these jobs' support effects leveling things out with all the buffs that followed.
I don't have faith in the devs actually gauging proper mechanics to such a role, given this games history, but that's why I do think they can start with the DPS aspect. A job that is still DPS, but has a focus on party output, rather than individual, which is something ALL roles and jobs are focused on.
For example, maybe it'd have reduced output like BRD/MCH by design, so an acceptable amount of DPS by itself. The party functionality however involves using an ability that sacrifices self output, for increasing a targeted party members output (not an aura, but a direct link). Say it reduces your output by 20%, but it increases a party members by 25%. Or if that's too potent, then 20% reduction on you but 15% increase with one party member. You can distribute that link to multiple members though, increasing overall output while you take greater hits to personal DPS for each additional link. 1 link - 20%, 2 links - 30%, 3 links - 40%, and so on while that bonus to party members remains constant (e.g. 15% increased output on each link).
THEN we can gauge interest properly on the idea of people helping the team, rather than focusing on themselves. I mean, think about how often BRDs/MCHs may not use buffs/debuffs or how often healers in pugs don't actually heal because they rely on the other healer to do it for them.