Obviously this is about Peyton Manning and Tom Brady, and the argument about which player is the better quarterback. I’m not going to reach a conclusion here, but there are two things that are important to consider that as far as I can tell almost everyone ignores.
The first is articulated by Benjamin Morris of FiveThirtyEight in his article here, which is that Peyton Manning was tremendously successful with multiple head coaches and even with two different franchises, whereas Tom Brady has been successful only with Bill Belichick and the Patriots. This isn’t a slight against Brady per se, but it does leave some room for doubt. Belichick did have Matt Cassel play quarterback for an 11-5 season after all, and had success this year with Brady suspended. Meanwhile the Colts went 2-14 the season Manning missed with neck surgery.
The second is pretty old hat if you follow baseball and read FanGraphs like I do, but as far as I can tell the media and other internet discussions don’t bring this up as often in football, and with the Super Bowl next week and this article from The Ringer being published yesterday this is a good time to bring it up: players’ value to their team is really their “market value” (if we assume the market is perfect, which it isn’t, but…) minus their actual salary. Over the course of his career, Manning was paid a lot more money than Brady (see for instance this Forbes article). Therefore, Brady’s teams have had a lot more money to spare to build a team around Brady than Manning’s teams have had to build around Manning. Even before accounting for Bill Belichick’s team-building ability (which as far as we know is the best in the NFL) this gives Brady better teammates around him, which then improves Brady’s statistics.
Of course, Brady has still had much more team success than Manning has, and their stats are very similar. I certainly wouldn’t be confident in saying that Manning’s career is greater than Brady’s. I just wouldn’t be confident in saying the reverse, either.