Well, I never watched that much TOS, but AFAIK yes minor. Certainly a regular, but rarely important. Could be wrong, but my impression is that Kirk Spock and McCoy are the main personalities, and the others are more part of the set, and not irreplaceable. Especially considering timeline.

I note my icon is of a version of Rogue whose history was vastly different from that of the comic book version. Versions.