The others faced the 17th, 22nd, and 29th ranked defenses in terms of overall efficiency. A lot of the debate on Flacco has revolved around the notion that he just wins. I hear a lot of people cite his overall win-loss record as a starter as well as mentioning he has a very good defense backing him up. On one hand he's been to the playoffs 4 out of his 4 seasons, but on the other he's not the reason the Ravens win.
Win Probability Added seems it was made to settle debates just like this. And WPA says that since his second season in the league, Flacco is one of the main reasons why the Ravens have been a winning team. In fact, over his entire career his WPA has averaged +0.10 per game. And his last two seasons were +0.21 and +0.19 WPA, well above average. In other words, his performance would make a .500 team a .700 team, all other things being equal. But not everything is equal. In particular, quarterbacks naturally have positive WPA simply because passing is more lucrative than running, plus it's been getting easier over time.
So let's compare apples to apples. I created a special version of the QB Career visualizations that only feature the four remaining playoff QBs. Here's how their WPA has accumulated through their playing careers. You might be surprised at Flacco's trajectory.
He's apparently on pace for the Hall of Fame. I'm only kidding, but keep in mind how slowly Tom Brady's career started. Brady was actually an average passer in the early Super Bowl years. His statistical explosion didn't come until 2004, when his Expected Points Added (EPA) tripled from the year before. This graph is a little misleading because Brady did not play his first year as Flacco did. Still, Flacco has improved over time just as Brady has. And as Brady was handed more weapons such as Randy Moss, Wes Welker, and now Rob Gronkowski, Brady's numbers followed suit.
It's also interesting that Flacco's trajectory is significantly above that of Eli Manning, who is widely considered to have developed into one of the best in the league.
I am not claiming Flacco is the next Brady. My point is this: Overall, Flacco is not among the current elite QBs in most ways, but he's better than most give him credit. He helps more than he hurts, and he's one of the several reasons for the Ravens' string of playoff appearances. And if his career continues with as much good fortune as it began, he could still develop into one of the league's premier passers.
Here's where you can find the full interactive QB visualizations, where you can choose your own set of QBs. Also take a glance at the "Nth Best" Career EPA page, which shows just how far Flacco would have to go to match the numbers of the game's best.
Full disclosure--I own a #5 Flacco t-shirt, and I'm sporting a very cool Fu Manchu this month.