I thought it was traditional for the HC to report to the GM, and would be typical for the HC to choose their OC/DC but probably consult with the GM. The owner is like a stockholder in a corporation - they would not normally hire staff. The GM is always consulting on HC hire/fire decisions as $$$ are involved and a major impact to the franchise.
What was the attraction of the Canada hire in the first place? Given the departure of Big Ben - who made two HC's look pretty good, Stillers are in a new position. They need OC and DC at a level who could be HC if needed. Pickens, Friermuth and Harris are the core of this team on offense. Take those 3 out and this offense would struggle to get 14 pts per game.