I’m inclined to mostly agree with you, but I think when it came to politically charged subjects there might have been some influence or attempts, particularly around left-wing issues, communism, labor unions, and civil rights topics.
Nixon had his famous Enemies List which was filled with journalists, and Nancy Reagan was in frequent communication with Los Angeles Times publisher Otis Chandler about the criticism of her husband (then California governor) in the paper, as only two examples.