Yeah well, you would have to take off the gel coat first to get to the barrier coat...which would pretty much be a bone-head amateur move (and an overzealous powersandin' rodeo). Beneteau posts that to prevent owners from doing stupid stuff. Overkill.Beneteau doesn't just recommend against barrier coating, they actually state that the sanding that the barrier coat manufacturers recommend before coating will void Beneteau's warranty.
If you want something to stick to gelcoat, either bottom paint, or barrier coat you are going to need to de-wax it and rough up the gelcoat to provide some tooth. Otherwise, sometime soon you WILL be sanding /scraping off flaking bottom paint.