As a little kid watching Star Trek reruns in the 1970s, I assumed that Kirk, Spock, and McCoy were the main characters and Scotty, Uhura, Sulu, Chekov, and Chapel were subordinate characters, as David Gerrold referred to them in "The World of Star Trek."
However, I did expect to see those subordinate characters each episode, at least if their position was used. I couldn't figure out why they paid an actor to be helmsman Hansen or DePaul when they could use Sulu, or why DeSalle beamed down to Omicron radiation spore world instead of Scotty or took command over Uhura in "Catspaw."
I didn't have to get much older, though, before I realized that it would have been stupid for Kirk to beam down with Yeoman Rand instead of a psychologist in "Dagger of the Mind," or that a sociologist like Lindstrom was necessary to the "Return of the Archons" landing party in a way that Sulu was not.
I guess "semiregular" may be the best term technically for the original poster in describing these characters, though you're not wrong as long as you don't call them equal to the three stars or just background characters with lines.