I agree with you about Dragnet (!!!). There was some humor in the earlier series, mostly on the part of his partner and usually earlier in the episode. I have some DVDs of the earlier ones but not the later ones. Some of his other productions had the same sort of mild situation humor between characters at the beginning of the episode but it certainly was brief. Overall, there wasn't that much variety between the episodes but the concept and format was limiting, though no more so that recent shows like Law and Order, for example.
Some of the longer running shows that I watched, like Bonanza and Gunsmoke, changed a lot over the years, which shouldn't be surprising, but they had a fair amount of variety in some of their episodes and some had a lot of humor, if not comedy.