The problem was that as the series went on -- they didn't write roles for supporting crew characters.
All landing parties needed was the big 3 and a disposable red shirt.
Then they didn't need the red shirt.
That's what I found disgusting-- guess what? -- Spock is an expert in EVERY field of science. Sociologists, biologists, meteorologists, botanists, geologists --who needs 'em? Spock knows that sh!t.