I love yapping about James T. Kirk

I'm nevertheless charmed at the idea of an Academy-era Spock and Kirk who actually look like young Leonard Nimoy and William Shatner—

—in those uniforms. Sorry JJ Abrams and whomever else, you will never take our heroes as baby-faced Starfleet teens in sparkles from me.

3— There is no officer/enlisted distinction in TOS outside of the Terran Empire of "Mirror, Mirror." Everyone on the Enterprise is an officer.

There's a pretty good discussion of it here, apart from minimizing the glaring differences from the real US Navy and, relatedly, the rather franchise-poisoned contortions around continuity/lore at the end. Its own evidence indicates that this is a very deliberate world building/thematic choice driven by the writers' and creators' grievances with their own experience of the US military and not just the Enterprise being special; they were pretty obviously trying to envision a half-familiar but better world, as far as their audience as they thought of it and themselves were concerned, one where the closest thing to a standing military is something like NOAA (then very recently consolidated into ESSA) rather than a full navy.

That definitely doesn't exclude WWII, the Cold War, and US policy in general militarizing the marine research agencies, and then expecting them to go back to normal but also be ready for combat at any time, but it's a different idea of the Starfleet "normal" than something purely naval—and, incidentally, NOAA's corps does not have an officer/enlisted distinction either (for context, NOAA has ~300 officers in the corps and ~12,000 civilians). The fact that we don't see the officer/enlisted distinction in any other Starfleet context in TOS except very specifically the Mirror Universe is, uh, a pretty standard TOS level of subtlety.

All of that said, the linked article very thoroughly covers pretty much all the arguments and counter-arguments around enlisted in TOS, esp on the Enterprise.