The same assembly line approach is what Ken Burns has being doing with his Docs for decades (he's finally sharing some credit). And, it also goes for most of Scorsese's documentaries. You can always tell if Scorsese is truly hands on if he himself is seen/heard asking questions on camera
Most of the early Danny Elfman "scores" were written in collaboration. He'd sketch out the basics by playing or even humming a few bars and then someone else would put them in score form.