Adam, when an attack coach is at odds with the head coach, you can be pretty sure the quality of the attack is more a reflection of that head coach than the attack coach. The only evidence I can draw from the Cheika years is that neither Cheika nor Gray were worthy of the title "coach".
Bernie Larkham was one of the best rugby players ever produced in this country. He played the pivotal position at No 10 which required more than any other spot the player to have an understanding of what was happening on the field the whole time. He had a great rugby brain, tactical nous and vision equal to anyone. His understanding of team mechanics is just what a head coach needs.
Despite the criticism often levelled at him for his coaching stint at the Brumbies, I don't think I'm wrong in saying he led the Brumbies as the most successful side in the country in that period.
Of course, if he'd played and coached as a Red he would be much more highly regarded on these threads.