One of the things I heard about McVay upon his hiring from personal friends and other redskin fans, was his inconsistency of play calling. He'd skew up brilliant plays, followed by real head scratchers, usually in the red zone. So if he didn't call the plays, it's clear that he's following the system he was brought up in, bc the stats and play calling decisions lean in that direction.
HC'S usually don't hire coordinators who have radically different scheme ideologies than the ones they want to implement with their team.