Sometimes it is, like anyone else. In the cases of Stan Lee and Jack Kirby, it was genuine. Stan Lee was creative passionate, and sometimes unfortunately, a ruthless businessman. Jack Kirby was talented, but working class. His parents encouraged his art to help keep him away from gangs. His trauma from WWII fueled much his output, like a form of therapy. Nowadays, he has been getting recognized as a legit great 20th century illustrator, with the art world's bias against comic artists going away.

Rick Rubin is a creative and weird mofo. I've seen my share of documentaries on albums he has worked on, and I'd say he's legit.

Likewise, Clive Davis pretty much stumble into being a record exec.

Most of the music guys, and all of the Hollywood guys (yes, even Spielberg), though, went in just for money, power, etc..