Monk has a high skill ceiling? Are you people delusional? "Keeping up DoT's and buffs" is no harder then any other job - DK/Demolish/ToD/Twin ? That's pretty standard stuff.. All 3 melee DPS have to do this..
As far as GL, losing GL isn't as punishing as you would honestly think. It takes roughly 15-20 seconds (less if you have PB, but PB isn't always ideal just to get GL3 stacks) to build up stacks again once you lose it (Roughly the same CD as Ninjutsu)... And keeping GL in most fights is about as hard as executing a mudra (so not hard at all, and often easier as FCoB fights are practically dummies). Sure there is the oddball fight such as Levi Ex or Ifrit (old content) where you will lose it during jumps, but jobs such as BLM have a tonne more fights where they are punished due to high dodge mechanics.
Ninja isn't "easy" for a lot of people either. While they still have the standard buffs to take care of (a few DoT's, damage/speed buffs), they also have to pay attention to near perfect timings with things like utilizing TA during the party's bursty phases, timing ninjutsu to squeeze in an extra Raiton, and keeping Goad on CD to support the MNK/DRG/BRD/Tanks (which MNK do not need to worry about.. spam your 2x sets of 3 skills over and over).
In addition to ALL of this - MNK is still the superior single target DPS.
Also the arguments about "SE's battle testers having played NIN far longer then we have" is folly. In the translation itself, Yoshi basically said that players are better then their internal testers, and that the current rotation for NIN (which was pretty obvious to most people after playing it for a short while) was different to those of the tester's. So it just shows that SE's testers aren't really great players. This is pretty evident after seeing some of those hilariously awful videos of them trying to complete primal fights in the early days.
While I am not one to say one job is "harder" than the other.. However to play a NIN well and use their utility in the right moment, takes more skill then spamming 2x sets of 6 skills on a MNK.
Finally I have never been a fan of this argument that SE keeps making as to why "MNK is so stronk" and that is because it has a "high skill ceiling". If that is honestly the reason, then make DRG more challenging to play well, and buff it on par with MNK.
Being a "harder job to play" is an extremely stupid excuse for having unbalanced jobs.