OK, it's important to step back from thinking of the Trek universe as existing separate from those who guided it and just accept that there was a sort of push and pull through all Trek's incarnations based on the powers-that-be.
That's absolutely right of course, and the points are well-stated. All I'm trying to explain is why, from the viewpoint of the work's internal consistency, I find the TWOK uniforms conceptually weaker than those of TOS or TMP.
C.E. Evans wrote:
Actually, it does, because things go in and out of fashion for whatever reason, and Starfleet is likely no different. If this was a period in which Starfleet became more militaristic in nature, then the choice of uniforms would reflect that nature. Conversely, the next uniform design (the original TNG uniforms), may have reflected a change in Starfleet's priority as an exploration agency.
That doesn't address the specific point, though. Before TWOK, enlisted personnel had a uniform that placed them, visually, in the same ballpark as officers. This is consistent with positive and progressive developments in the 20th century that recognized the value of all service members' contributions and attainments and sought to minimize former class/status based differences. Then suddenly in TWOK, enlisted members were put in uniforms drastically different from officers and which overtly emphasized the fact that they were of lower status. That implies an immense change, even reversal, of the organization's structure, culture and core values. A switch in emphasis from exploration to defense does not seem nearly enough to account for it.