Damien

Actually, that reminds me of another issue with that Beatles episode: The Beatles were almost incidental to the plot. There is so much interesting Beatles history they could have interjected the Doctor into but they are really only there to play that chord.

Think of how well an earlier season handled Van Gogh. A real strength of the show has been the alternative stories rooted in real history. You have a big historical figure or event, but something disrupts the timeline, and the Doctor goes to fix it as an excuse for the writer to explore that character or event. Do that more.