As a BRD main of 3 years, I can tell you that that's not how that works lol
Currently all ranged dps (including bard and machinist) are being far, far too low purely because the support tax is way too high and the dps we give to others is way too low. Despite being pretty much amazing in Stormblood, you didn't see 2 Bards in a party either, yet they could keep up a fair deal. Because Bards themselves do not benefit as much from their own boosts, they *give* boosts. I recognize that by the end, Bards were hilariously overpowered, but that's a matter of crit scaling exponentially twice on Bards, which has been dealt with accordingly. Dancer doubles do not particularly buff the party as well together either, and the myriad of other issues coming with this do not help either. Your analogy does not hold up.
As for the RDM/SMN dps problem, here's the deal. It does not have to be as strong as BLM, ever. In fact, there have to be a couple of jobs like BLM to keep the 4-dps balance of the game in check. The game is supposed to be played, according to anecdotal evidence inferred from how the duty finder and party bonus mechanics work, by bringing a healthy mix of jobs from ranged dps, caster dps and melee dps. Then there's 1 slot left, which is usually reserved for bringing a ninja or another selfish dps, or something for a somewhat specific party build.
However, simply having access to raise and to a lesser extent, vercure, does not warrant being essentially worthless otherwise. Neither does bringing some defensive support type moves. RDM doesn't have to be as strong as BLM on its own, it has to thrive off of bringing other selfish dps, or be closer to it in general. Being 80% isn't a fair exchange for having access to some support. That should be more like 90% in the case of RDM. In the case of Bard, Dancer and even Ninja, they should be more like 85% turning 95-102% when coupled with selfish dps types. Machinist should be 93 to 98% to begin with, Summoner should also be around that.
All of this should prevent the meta from turning into "just bring the top 4 dps, they're so strong the 1% main stat buff from party bonus won't even matter".
And by the way, if you want to get technical about it, everything has support in a way. Black Mages have Addle. Monks have Mantra. Samurai has Feint (Thanks person who reminded me <3).
As for when people get them on farm, RDMs won't be throwing cures and raises, yet they'll still be taxed to hell for having them so nobody will want to even bring RDMs or even SMNs. This is why raise tax needs to be drastically lowered. Yes, in it's current iteration, RDM is fated to be one of the lowest DPS. That should not make them borderline unplayable in pug settings, though.