It is one reason, I think, that a team trading for Garappolo needs to beware.
The Pats have been designed around the QB. They are a well oiled offensive machine. And of course, a very good defense.
Put Garappolo on a poor team, and then expecting him to elevate it, would be a mistake.
There are QBs who can elevate a team, however. Brady, Rogers, Peyton Manning come to mind.
But even these guys can't make a poor offense with a bad olline, bad receivers, and kindergarten offensive schemes work.
I heard interesting draft debates about the two opposing philosophies on drafting a QB high. The thought is that if you have a very high pick and take a QB, you are bringing him to a bad team and putting that QB in to an unwinnable situation. And it is unlikely that the QB is going to do well until the rest of the team is better. So you might be dooming that QB from the get go. Bottom line: build the team first using back-up quality vet QBs until the team is a QB away from getting over the hump.
The other philosophy is that if you are a bad team, no doubt QB is high on your list. And you do what it takes to get a good QB. And then you develop the QB and the offense together, knowing that you're going to go through growing pains for the entire offense.
I see the merits for both, but really doubt one way is better than the other. They key is to recognize what you are and to have a plan. The always delusional Jeff Fisher honestly felt that the Rams were just a QB away (geesh). But clearly he had no plan to develop Goff or an offense. It was throw it against the wall and see what sticks.
McVay clearly has a plan and it began by shoring up the offensive line, and next getting some Receivers, coming in with a QB friendly scheme, and then by developing Goff the same way he did Cousins; step by step.