I haven really watched more than a few episodes of ToS, but IIUC it never even bothered to be a realistic depiction of how space exploration would look like. It was more e metaphor of the Cold War, in Space!

The original series was rarely about the political or military tension between the Federation and an opposing major power (i.e. the Klingons or Romulans). It was much more often about dropping in on some planet and solving some local problem; or some psychic effect or setup by superhuman powers causing the crew to reenact a moral or metaphorical drama. Superhuman godlike entities appear more often than the Federation's rivals.

(Klingons only appear in seven TOS episodes, and Romulans in three — out of 79 episodes produced. Alternate Earths, such as those of "Miri" and "Bread and Circuses", and explicit reenactments of Earth social systems, such as the Nazis of "Patterns of Force" or the gangsters of "A Piece of the Action", are about as common.)