I think that, while being a reasonable opinion on paper, is fundamentally flawed when you see how Stormblood "meta" went. Selfish jobs were ignored/kicked out of party because they "didn't bring enough to the table". While I do agree that there shouldn't be that much of an advance in rdps for every job, the general playerbase sadly don't think like that. And a Black Mage that deals just the same amount of rdps as a Summoner will just get ignored in pf, because "summoner does the same thing but it's easier, and it has rez".
We've seen how the "synergy" meta went, when everybody had raid buffs and the selfish weren't that much ahead. Then suddenly the "selfish" jobs become much less interesting to have in your pf because every other job could do the same AND buff others.
On the opposite now, in Shadowbringers we've reached a point where in pf it doesn't matter what class you play. As long as there isn't a trio of the same role (triple melee/caster/ranged) everybody is happy and content gets cleared just fine (well depends the skill of your pf. It's pugs after all).
Still I do agree that maybe summoner is a bit high when compared to red mage right now, and that bard should probably get something better, at least to put it on par with dancer in terms of rdps. But I do not think that nerfing the damage of selfish jobs will do any good to the way the meta is seen by players. Or then you'd have to change the playstyle of samurai and black mage. Because seeing how difficult it is to get really high with those two jobs (especially the current sam design lol), lowering their output to bring them on par with the other jobs would just mean that bad/decent BLM or SAM will suffer even more from this nerf, as there is currently quite a gap between the highest and lower percentiles.