That everyone on the Enterprise in TOS was an officer. Silly. Just damned silly and impractical.
I can buy GR's thinking on this. TOS was made in the era of the NASA astronaut-hero, the days of John Glenn and others. At that time, all NASA astronauts were college grads and all were officers.
GR wanted his TOS crew to be qualified astronauts, same as NASA, only in a future century. NASA only had officers as their astronauts, GR wanted no less. So okay, everyone on the Enterprise is an astronaut and an officer.
I totally get this, and understand how GR got to where he got. and that is totally huny-dory in a Gemini or Apollo capsule with two or three guys.
However, this ain't gonna work in a large fleet of vessels, or in even one vessel with a crew of hundreds. you have to have a solid chain of command in place and you need it to have a very definite structure. Despite the fact that Picard seemed to run his ship by committee, I think it is a very bad idea. You need to have management (commissioned officers), middle-management (non-commissioned officers (i.e. petty officers or sergeants)), and the workforce (enlisted crew). This does not make the "lower" end of the scale any less important or valuable, or the upper end (officers) necessarily any more so. They just serve a different function in the overall operation of the ship/organization.
You can have highly trained and skilled crewfolk that are enlisted. Look at the enlisted people in today's military that do some very technically complex jobs. They didn't need to go off to an academy for four years to do that. And most of the people you see on a starship wouldn't either for the jobs we see them doing.