I've been saying for years that this whole "comeback drive" thing is the dumbest stat in the history of the league.
If your team scores a go-ahead defensive touchdown with 14:59 left in the 4th quarter of a previously tied game it counts as a "comeback win" for the quarterback, just the same as if someone drove 80 yards in the last 53 seconds and threw a touchdown to overcome a 4 point deficit. It's ridiculous.
And really, even if you look at "true" comebacks, it's still a ridiculous stat because worse quarterbacks naturally get more attempts. You look at a team like Pittsburgh or Baltimore, who spent years with great defenses and bad offenses, and of course they're going to have lots of "comeback" wins (because of more comeback opportunities) given that broad definition, since pretty much every game they go into is close in the 4th quarter BECAUSE of their inept offenses.
A guy like Drew Brees isn't known for his comeback wins, and he doesn't have any this year. A big part of that is because against many teams he's so far out in front he never gets a chance. You could put a mediocre/bad QB on the Saints and they could very well have two "comeback" wins this year, but Brees has none because he's good enough to be up by 30 points in the 4th quarter of those games, and as a result when people start comparing the top quarterbacks he immediately gets pushed down the list. It's like saying he's not as good as another quarterback because he's TOO good, which doesn't make any sense.
And the real story here, as I believe someone ran the numbers a couple years ago, is that if you look at the stats for comeback wins in their TRUE form (IE real comebacks, based on percentage of opportunity where they had the ball, down by 1 score or less but not tied, with under 5 minutes to go in the game), Rex Grossman is one of the most clutch quarterbacks of our decade.
But no one throws that stat out there for Grossman. Why? Because people only use comebacks in their fake form, to make up for a deficiency in their argument elsewhere.
It's like Pittsburgh. People love to bring up how Roethlisberger has this ridiculous number of comebacks for how young he is. Well of course he does, with that defense and poor offense nearly every game that Pittsburgh plays is a one score game in the 4th quarter, so there are tons of opportunities. Most of the games that Pitt loses are failed comeback attempts, but no one ever talks about those.