I will take a different spin on this. I don't think it was the people so much as it was the overall system he used. It looks to me like he was a drill guy - meaning you work on your technique in drills more than live work. It looks like, and I could be very wrong on this, that they have O linemen working footwork and hand drills with less emphasis on live blocking if that makes sense. When we get in games we can't pick up a blitz or move as a unit when blocking. On D we don't flow like a cohesive unit. To me that goes on the head coach. The assistant coaches are doing what the head guys wants.
I am sure to be in the minority but if I had to point to weak areas - I would start with Riley in overall organization and detail of coaching, Cav, Diaco is a disaster despite the excitement on here when he was hired - so how did that "opening of the check book for assistants" work out?
Langs was pretty handicapped trying to call games with no running game because the line couldn't block my mother. Riley knows he needs to run the ball better but they simply cannot and everything feeds off of that. Riley felt this system worked in the past and if he had better athletes it would work better - again, this is just me guessing which I don't like to do. It is obvious he hasn't changed his coaching and the results in this league are much more difficult to come by than the pass happy Pac 12.