Seems to me that there was no single problem. DJ was one of them, and not because he was a bad guy. You don't fire your OC and release your LT two weeks before the season. That's just a recipe for disaster. That is all DJ.
You also don't mess with personnel the way DJ and Brandon did. You can't have upheaval on the O-Line through an entire offseason and that was what was engineered by the front office, probably with input from DJ.
You also don't mishandle the quarterback situation so badly that it not only becomes bad, it becomes dysfunctional. Awful.
So it clearly wasn't all DJ's fault, but he was certainly a factor. The fact that Brandon didn't get fired is disconcerting to me. He clearly had a role in this mess. It is good that he is supposedly out of the football decisions, though.