Even advanced metrics struggle to accurately gauge just how valuable an elite quarterback is to a particular team. Over the past nine seasons, the Colts have won 13 more games than their points scored and points allowed totals would have predicted, outperforming their Pythagorean expectation in every year during that stretch. The only team that's come close to that over the past decade, as you might expect, is the Patriots. They have exceeded their Pythagorean expectation in eight of the past 10 seasons, accruing 8.1 extra wins. (Although you might expect that one of the years they came up short was the Matt Cassel season in 2008, that wasn't the case.)
I haven't been able to find a similar case in recent history. Joe Montana's 49ers teams exceeded their expected total by 4.7 wins, but they didn't reach their expected total in four of his 10 seasons as the established starter. Dan Marino's Dolphins teams were eight wins better than expected, but like Montana, the teams failed to hit their Pythagorean expectation five times. John Elway produced 9.9 extra wins as the Broncos starter, but his teams also came up short five times. No single quarterback in league history has ever been able to pull off a stretch like this for more than six consecutive seasons. If Manning isn't around, it's hard to fathom how the Colts can exceed expectations for a 10th straight year.