Well, using Rubin as an example of getting Paul to maybe do a stripped down album of acoustic (and maybe rock) songs. It doesn't HAVE to be Rubin, but his rep and his ability to work with and get the most out of superstars is pretty evident.
Listen to what he did with Neil Diamond. I always HATED Neil Diamond. But, the two albums Rubin produced for him are fantastic.
Cash's SUN work is great. Not that familiar with all his stuff over the years, but he got kind of hokey at times, and wandered aimlessly for awhile. I think Rubin (and I'm sure Cash had as much input as Rubin did) got Cash to go as far back to basics as possible. Cash has (well, had) always been pretty genuine, pretty honest, pretty sincere. Rubin just was able to translate that even better thru the music.
Just my opinion.