The least played jobs, based on logs and more I’d say,

Monk - least popular
Ninja.
Red mage.

Ironically against popular opinions, summoner is actually 4th highest logs recorded.

Although many dislike summoner people are still persisting with it, it’s had a large audience for a long time which a lot won’t betray in hope for changes in 5.05.

Red mage popularity has died a lot, I will presume this is mostly because dancer got released, reading a lot of forums a lot of RDMs moved to dancer due to how much more fluid it’s procs are as they stack and more which makes it flow even smoother then RDM

And ninja, the most complex job in the game, not many play this job even during its best times, this is because the job just is a very highly demanding role for the worst dps in the game. Due to its RDPS although I’d say it’s very much too low. It’s not even on 1000 RDPS currently so when adding these things up it’s just not worth it currently.