The biggest problem Stevie Wonder had in his heydey was his insistence on the use of a keyboard bass (played by him) as opposed to a human bass player. The lack of improvisation in the bottom end of his tunes was the death of his artistry. Obviously a great songwriter, but way too full of himself to be a lasting icon. True genius recognizes when it needs assistance.
Say you want to hear the difference? Listen to Talking Book with an excellent real live human bass player and then to Hotter Than the Fourth of July without. I think you'll understand.