that is a little misleading though, because then what you are really doing is putting all the emphasis on the backup and surrounding teammates or the difference between the starter and backups and surrounding teammates. in the 90's and even 80's we just 'reloaded'. so even though we had incredible starters, we did not really lose a step with the backup in. i do agree that the players you mentioned are some of our all-time greats and that they elevated our team more than probably any other player, but the caveat would be that the players around them had a lot of room for improvement.
i will put it this way, given your criteria, zac taylor should be considered an all time great. and maybe he should, but the point is that the team would have been significantly worse without him.