Put Don Adams with the list of TV leads.
Della Reese was on there, but it was about 10 years before she became a TV lead with that series where she was an angel (she was also about half as big as she was on that series).
Didi Conn was in some movies, including
Grease
, but not a lead.
Jamie Lee Curtis was on in 1980, which would be after
Halloween
, though she became a much bigger name after
Trading Places
three years later.

Michael Landon & Jack Klugman were pretty big. Sure they were TV stars but they were leads. A lot of Match Game contestants were TV supporting players.
No! That's not true at all, Elvis takes 50% of everything I earn!
Col. Tom Parker

Patty Duke won an Oscar for her portrayal of Helen Keller in "The Miracle Worker".
Ethel Merman was a huge star on Broadway and also made some movies, I believe.
There were other guest celebrities who were not actors but were enormously successful in their own field. Professional baseball player Don Sutton, country music singer Bill Anderson, and household name psychologist (or was she a psychiatrist?) Dr. Joyce Brothers are some that come to mind. Dick Martin was a TV star, that's true, but he was the co-creator of "Laugh-in" which was a huge cultural phenomenon and he was probably worth millions upon millions of dollars by the time he appeared on MG.
But yeah, you're right, most of the guest celebrities were just TV stars from that period.