You even said it yourself, unless they rid of those buffs or MNK gets something essential, two things that we've no idea will change. We can't necessarily say it won't change either just because lolSE, especially considering MNK was a princess job all through 2.0 (hi double MNK parties) while casters fell out of favor mid 3.0.
Going off of the current meta setup (DRK/WAR/DRG/NIN/MCH/BRD/AST/SCH), DRG is the only job that doesn't have to worry about competing for gear with NIN behind it since it only has to compete with right side. With 4.0, the worse setup for gear distribution would be Tank/Tank/Heal/Heal/BRD/MCH/MNK/SAM since everyone would have to compete with someone else. But I mean, no one would run that setup right? It's silly to 100% say yes or no. Resists might go away or be shifted around, MNK might get magic resist down or an increase in DPS that makes up for the lack of raid utility or even get actual damage raid utility, or SAM might synergize better with MNK that it does with NIN/DRG and a SAM/MNK combo would be > NIN/DRG.
Honestly though, I would rather SE get rid of maiming/scouting/striking and just combine it into one set then along with the other sets (fending, casting, healing, aiming) allow us to customize it depending on the job we're using. You'd have to compete for gear early on but it would get rid of wasted gear later on. Or streamline gear even more and just make heavy armor, leather, and cloth along with being able to tailor it to the job somehow.