although I do agree that 'most' of the time losing a starting QB will result in failure I'm not sure it's 'rare' for a backup QB to "play as well, and rarely better".
That would be very difficult to assess... for example... you lose a starting QB going into the playoffs and then the backup QB loses in the first playoff game, or the second... who's to say the starting QB wouldn't have lost as well? Stats? I dunno... once in the playoffs you're facing much better teams than the average team faced in regular season.
I'm not saying you're wrong, by the way... just saying that personally I'm not so sure. Surely there are several, (not most) backups that are as good and perhaps better than the guy ahead of them. And I'd add that a significant reason backups usually don't play as well is due to being ready... time on the field, not necessarily because they just aren't as good. - JamesJM
