Because I don't really follow current music, I wasn't sure about weighing in here -- but here goes. First, I agree with the way that you've compared the three artists, and everything you've said makes sense to me. The one thing I'll add is that I think Swift has had sustained success going back to her first album in 2006 and that it has kept growing over the years. I consider that to be a more impressive career arc than Elvis, given the downturn that he had from 1964 to 1968 and the fact that his last big hit came in 1972. As for The Beatles, the most comparable member would be Paul McCartney, who continued to consistently have major hits throughout the 1970s and into the early 1980s. But to compare this with Swift at the same point in their careers, I think that she's having even greater success than he was having when he was 18 years into his career. And with her still only being 34, she also has the potential to continue to be a huge star for many years to come.

He was probably best known for reaching the top 40 twice with "Something's Wrong With Me" and "Rocky", but he had a lengthy career in music which included major successes as a country songwriter. 
https://williamsonsource.com/obituary-george-austin-robertson-jr/