As a naive kid I thought that she didn't make captain because she was nuts. As an adult I realized that at the time it was a stretch that there was a woman, and a Black woman at that, on the bridge crew. A female captain would never make it past the producers.
It may be a retcon, but Uhura was not Command Path, just like McCoy and Scotty. Both Sulu and Checkov were in the Command Path, with Checkov becoming first officer of the Reliant and Sulu taking command of the Excelsior. Scotty does become a Captain, in The Search For Spock, taking equal rank with Kirk and Spock, but he is not a starship commander. He's "Captain of Engineering" instead.
Also, Uhura seems to be in a dying profession. The Communications Officer is dropped and merged into other positions in the TNG era.
You need to view it through the lens of the time, not today. At the time it was a huge step forward in network TV.
There is no sense of place or time, since there are no limitations. It is limitations that separate "sci fi" from "sci fa", and these writers are hacks that simply don't care.
In TOS they weren't replicators, they were food synthesizers.
What’s the difference?