What hasn’t been mentioned here yet is that Johnny Carson was great when it came to doing physical comedy .. whether it was pratfalls, sppearing in his jockey shorts, wearing some kind of crazy costume or outfit, etc.
Carson was in the same class as Lucille Ball in that regard.
Leno, Letterman, John Stewart, Conan O’Brien (I hate how he always messes with his hair, that’s his big schtick?) are just stand up comedians, and not very good ones at that.