O’Brien is a “chief,” Jonas and Cutler hold the rank of “Crewman,” and I think those are the only enlisted personnel who have lines and appear in more than one episode. Starfleet seems ridiculously officer heavy.
Is the enlisted/officer distinction different in Starfleet from traditional armed forces? And where are all the warrant officers?
I saw a video once that said, for the size of the Enterprise ships, the onboard populations are actually really small. Presumably the various departments and quarters are distributed throughout the ship and it’s just very sparsely populated. Doesn’t make much logistic sense to me, but if they had everyone centrally located with the usual crew size, much of the ship would have been empty.
Edit: video
The Enterprise-D could probably accommodate about 3-5,000 people if pressed to. It had a ton of space for cargo, evacuations, ferrying and/or hosting diplomatic conferences… TNG often makes passing references to these missions, but they often happen off-screen.
Which does make sense too, since the federation seems to like their ships to be prepared for just about everything, including massive evacuations.