Despite (or because of) being a James fan, I don't give a lot of credence to his memoir. I know the portion you're talking about; you have to remember that 1) Rick could say whatever he wanted in his memoir, and 2) it was well known that Rick had serious drug issues. It was less known but still known that he had beefs with other artists, too... he admits in his book to being jealous. The guy was a super talented musician who was also a hot mess.
But even if Prince did copy shticks or whatever from James' show, so what? He was and is far beyond being a Rick James clone. Simply google "Prince 1980" to see how different his look was, and the music speaks for itself (other than being under the broad umbrella of funk/soul, their music sounds very different to me) -- Prince was an innovator.
Everyone borrows in some manner from what came before them. The idea that Prince was/is some copycat hack simply does not reflect his music/image/career.