People liking its gameplay wouldn't mean much if it wasn't also one of the best jobs to have in your team. People liked RDM, but once it became more cemented that the job was really only good for progression, it fell off. People liked SAM and BLM, but again, as more and more people realized that they didn't bring the adequate damage to compensate for the fact they're not team players.
Conversely, lots of people dislike SMN. They like the idea of being a SMN well enough, but they hate how SMN has been implemented in this game, and there are always criticisms of its gameplay whether that be its awkward three-segment-rotation, bahamut not being responsive enough, and egis being underwhelming. In my experience, it's about as clunky as MCH. Yet, because it brings the damage, it's the most played caster, even after nerfs blowing RDM and BLM out of the water and is the fourth most played job this tier, right behind the Meta Three.
At best you'll see a handful more MCHs...and a lot of people who prefer playing MCH will be able to justify to themselves their desire to play their favorite job to their party, instead of quietly swapping to BRD themselves because of how much better it is for its own slot.Nerfing BRD won't change the landscape right now whatsoever because people dislike MCH's gameplay by and large. Will you see more MCHs? Sure, but the numbers aren't going to swing from 43k BRD to half that. Nor will MCH suddenly balloon upwards. At best, you'll see a handful more MCHs. And even that is being generous given how universally disliked the Stormblood iteration has been. A nerfed BRD will still be overwhelmingly preferred for its gameplay.
This is like saying SMN shouldn't have seen a slight nerf at the end of Sigma because it didn't immediately make BLM or RDM the most preferred jobs. No, BLM and RDM aren't suddenly as or more popular than SMN, but it's a damn sight easier to justify being a RDM now because I'm not dragging rDPS down by a huge margin when playing my preferred job. Even then, it was only a slight nerf to SMN, and a buff to both RDM and BLM--something the likes of which could be done for MCH in relation to BRD.
It was meta because the casters were garbage through most of this expansion. What flavor of garbage did you want, the turret that needs the whole party to adjust to it and doesn't reward the party for strategies that do so (BLM)? A slightly less turret that did less damage than even BRD at certain places (RDM)? Or a jumbled mess of mechanics and spells that the devs kind of barfed up and hoped was good (SMN)? ...or perhaps, Machinist, who not only didn't need to be adjusted to, but was just as mobile as bard, but enhanced bard's burst potential and increased healer damage potential even more?My point was MCH was meta at varying points this expansion; both throughout Deltascape and into early Sigma. Dismantle was also considered better for UcoB. Despite its highly competitive status, people still wouldn't play it. MCH spent all of Deltascape dead last in terms of popularity. Hence why nerfing BRD, which I don't inherently disagree with, won't change the landscape.
Notice into Sigmascape, Summoner was what overtook Machinist. Summoner was fixed up a bit and given a gigantic damage upgrade, getting close to being the highest damaging job in the game. As well, whenever Machinist buffs are brought up, it's casters who need to be considered because they're the ones MCH would compete against--not BRD. Which brings us back to...Machinist cannot be buffed, but its competitor apparently cannot be nerfed.
I wouldn't say it's the casters that are OP in this equation. When MCH has to fight for a completely separate spot in the team than BRD, despite the intent being that it competed with BRD, I don't think it's the jobs that traditionally fight for the fourth spot that are to blame.