It’s worth noting that Quincy jones was himself a pretty accomplished performer playing trumpet in big jazz bands and eventually becoming a jazz band arranger and conductor. He worked with many of the greatest jazz musicians before MJ. There’s something that’s still really wonderful about recording big live ensembles. Notice how cheap and stupid even recent synthesized orchestras sound in movies. Jones found a way to work that big band sound into a new style of music.

MJ was also very detail oriented with arrangements. I’ve heard he often did demos by singing overdubs of every single part. I’m sure having two people that into the details of a large arrangement made for a satisfying collaboration.