I think Roddenberry's idea of everyone being an officer makes sense if you think Starfleet less as a navy and more as NASA. Everyone aboard is a highly trained astronaut. However, no-enlisted got already contradicted in TOS, so that's bygones. Then again, I think it is mistake to assume that Starfleet operates completely like modern militaries, it is combined military-scientific-diplomatic service and is not directly analogous to any modern organisation.
In one of his last interviews, Roddenberry said that he had been influenced by the Robert Heinlein book
Space Cadet, in which the Patrol that policed the solar system was composed only of officers and officer-cadets. Which, even if he hadn't contradicted himself in TOS, is fine, but ignored a couple of things: One, the Patrol was complemented by space marines which had a traiditional enlisted structure, and two, the Patrol's ships only had a crew of a dozen or so.
I think the "enlisted" component by Star Trek's day would likely be so technically skilled that they would be almost like a parallel specialized set of officers without broader command responsibilities. Which is indeed already happening today for senior enlisted. In the early days of spaceflight, there would be no need or room for unskilled labor and the service would evolve from that. In our current US terminology, Starfleet might be more like a certain number of commissioned officers, a larger number of warrant officers, and a smaller number of entry-level, in-training enlisted.
I often think that there is probably more of a "developing yourself policy", I think Starfleet - due to having no real limits on size of fleet and amount of personnel, insist that a Fleeter is "competent at their role, and improving their skills if needed to reach their highest "point of competency". So Tapestry!Picard who is a competent analyst but lacks the confidence and drive need for command can stay at the lower ranks (Barclay for the most part would be similar), but by contrast officers like LaForge, Crusher, Troi and Pulaski can advance Chief of Department and stop there, and Captain (even potentially "Skipper", holding more junior rank) can be held for years or decades for those who want to be at the "frontlines" because for the most part new ships/slots are made available fast enough that no-one is "held back" even if someone doesn't progress.
How would that even work? First of all, I know the Federation is expanding, but there has to come a time when they have all the ships they can use. Second, each new ship has to be crewed with its own little pyramid of lieutenants, JGs, ensigns and so on. That means more slots needed for them to move up. If nobody is forced out, that means more ships built for them to advance, which means more officer positions needing more slots for them to move up and so on and on. Unless Starfleet exists first and foremost to provide career advancement for officers, it doesn't seem plausible.
I know that there were examples of COs of the same ship for 20 years, etc., but IMO those were written without thinking through all the implications and aren't very realistic.