I’ve long held the belief that Lucas’ real passion for filmmaking was in editing. Just look at how excited he is in the TPM doc about how digital tools let him blend together a performance by actor A from one take and a performance by actor B from another take in the same shot.
Lucas is a great big-picture idea guy, an average writer and director, and a fantastic editor. I also think he would have personally edited every Star Wars movie if his duties as producer and director didn’t make that pretty much impossible.
Him hiring Burtt for the position of editor on the PT certainly lends credence to that idea, since Burtt to my knowledge was not exactly known for his (non-sound) editing skill at that time.
It seems to me that Lucas picked an in-house buddy for the position precisely so he’d be able to backseat drive like crazy.