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?
Or just making the hallways seem fuller with different background characters rather than the same characters roaming the mostly empty hallways.
The Galaxy class really is that big though. The Severance levels of isolation in the hallways would actually be reasonable for its size.