Does the backup QB really matter?

[fredtoast]

(09-01-2016, 11:09 PM)Shake n Blake Wrote: Look, the kid was managed. The offense was clearly pared down to protect him from mistakes.

Yeah, that was  a brilliant idea to have our running game only produce 68 yards against the Forty Niners and 155 in two games against the Steelers when McCarron was under center.  Maybe if we had went all the way down to zero rushing yards McCarron would have had a 120+ passer rating.  

So why doesn't every other team in the league just "pare down" their offense and make their QBs produce 97+ passer ratings if it is that easy.