But if rank is just a title as Roddenberry always insisted, maybe he wears the rank to fit the job he's performing, rather than his 'actual' rank?
Roddenberry's quote was that, in Starfleet, "... rank is more like a job description".
Ah, thank you.
So then it does fit that Kirk would have a different title to command a starship than he would to serve as Chief of Starfleet Operations.
Doesn't really explain Commodore Decker commanding the
Constellation in TOS though. Why shouldn't he be a Captain too, unless he was a fleet commander of some kind?
Indeed, it makes me wonder if Kirk could have retained his Admiral rank and still commanded the
Enterprise if he were commanding, say, a task force?