Yes, I think he was. I can remember Johnny mentioning that on the show. Even if I wasn't staying up for the entire show, it was essential to listen in to the monologue. Water cooler talk the next day...lolCavett's shows were different than those of the other three, more intellectual and thought provoking. I still remember his interviews with Groucho Marx and Mohammed Ali.
I think Cavett was a writer for Carson early in his Tonight Show tenure.