Yeah, I get that. Your last comment was odd. McVay has went a few years without an OC, so he was the OC/HC, but I'm sure he delegated most day to day OC stuff to his position group coaches, etc.
I do agree, guys who act more like Coordinators and not HCs don't last long. Sirianni had to relinquish his meddling and let KM do his thing for the Eagles to get over the hump.