Sometimes it's not that clear cut. Brian Wilson post Beach Boys may have an artistic edge, but certainly not popularity. Frank Zappa post Mothers Of Invention by volume alone overwhelms the earlier work.
Nile Rodgers production work after Chic is vast and very impressive. Bill Nelson's work post BeBop Deluxe could be obscure, but reached heights that the band did not. Janis Joplin was certainly most popular as a solo artist after Big Brother & the Holding Company. Elvis Costello as a solo act has released a number of superb recordings throughout his long career. Curtis Mayfield achieved greater fame as a solo act than with the Impressions. Finally, Mick Taylor's s/t debut album is far better than his output with the Rolling Stones. The songs weren't up to the Jagger/Richards level, but the performances were better. Unfortunately, he never reached that level again.