i know i'm biased because i'm a big fan of gouche's...he's one of my biggest influences! i can definitely see how one would call his performance overplaying if you aren't familiar with his work or background.
the thing is - everything he did is exactly what he does! the licks inbetween the spaces of the vocals, switching up the original bassline, starting a bar on a note other than the root, thats all classic gouche. he's an innovator with all of that...its his style of playing. if someone hires gouche for a gig, its because thats what they want. you wouldn't hire victor wooten for a gig and then get upset because he plays a wooten lick - its what he does. andrew gouche came up in the black church, where showmanship is really a strong part of the repetoire, esp. for bassplayers and drummers. if you aren't too familiar with this, you may think that the playing is stepping on the vocals, but alot of singers in that genre love that call and response interaction with the band, where different instruments may fill in some gaps in the song.
also, i'd have to side with him over prince because its his gig. essentially, prince and stevie were just sitting in with chaka's band, and gouche is the musical director. he most likely put together that entire medley, and then the other artists that were in the tribute just came to the last rehearsal to fit in where needed. (okay prince, you play a solo here...stevie you're gonna sing this verse, etc.) so i don't think its prince's place to expect gouche to change up his style of playing on his own gig. if prince had hired him it would be a different story altogether.
once again, i know i'm biased, i know andrew and he's a not just a great player, but a great person. i just wanted to give a bit of context to his playing...