I suspect McVay's comment was made out of frustration, and came at a time not too many hours remove from a disheartening playoff loss to a coach he really wanted to beat. (If rumors are to be believed) I suspect that he may have given a more diplomatic answer if he'd had more time to process the loss and his feelings about Goff's role in it. I doubt he would have even have been asked the question if the thumb/benching issue hadn't happened previously.
As someone else pointed out, Snead's comments are more questionable. Was he backing up McVay since Sean had started the ball rolling? possibly. Then again, Snead is generally pretty smug cat-and-mouse any time he has information he might share or withhold.
Is Stafford an upgrade, short term, I'd say "yes". Long term, who knows. But the team seems to operate focused on one season at a time, so he does fit their model for continued success.