Curly I also agree with you that William & Catherine are trying to pull back from the celebrity line. Diana was very unique, she was the first British Royal to cross deep into celebrity territory where she really fed the media too and used them to “control the narrative” as it were.
I think William has recognized you’re playing with fire if you play that game and seems to be trying to consciously position him and his family more carefully. He seems to be taking the Queen as more of his role model in that regard, be warm and open when talking with people but keep a certain distance with the media.
I think maybe the more recent seriousness that a lot of people are commenting on is he is so aware that now he is raising, and responsible for, a future monarch.