It's weird with MJ. His biggest issue wasn't his talent, but his refusal to adapt to change.
He clearly was VERY involved in some of his best music. He was very involved in a how song is composed a certain way he wanted it to sound. It's one thing to study music theory; it's another to properly incorporate it and bring out the best elements of multiple sounds to help create that song. And for that, the work he did with Quincy is imo, genius. It's something people hope to create time and time again but have failed. The problem is that once he found a certain sound that gave him his pinnacle of success, he wanted to stick with it even though the zeitgeist had changed.
I think sometimes who you work with helps to bring out that genius with you. Hell, Quincy has worked with a multitude of artists, but he has never been able to replicate that kind of timeless music that he created with Michael. There was a certain type of synergy and creative genius that was involved in their process.
Clearly from watching This is It, he didn't need help on the performing aspect. When it comes to performing, and the thought process behind it, he has no peer. Musically, he clearly had a vision and involvement, but it doesn't reach that stroke of genius, unless he has someone who can bring it out of him.
You can be genius and be stubborn and resistant to change. And to me, that describes Michael.