It's true that all your average fan has access to see, or the will to see, is stats. And it's true that stats don't tell the whole story. But they do a better job of painting an overall picture of a quarterback's performance than relying purely on physical traits
What we have here is Oldfan saying that performance doesn't matter, basically because a quarterback's performance will be heavily influenced by the system and the coaches around him. The issue is that it treats a quarterback as merely another cog in the wheel.
It doesn't take insider knowledge to know how heavily Tom Brady (I know I keep hammering on Brady but I'm not defending him so much as making a point) influences the offense, particularly over the course of the last 3-4 years. The Patriots didn't even have an offensive coordinator in 2009 and 2010. Brady was, for all intents and purposes, calling his own plays.
It only takes a Google search to understand how the Patriots no huddle system works. The Patriots system is, basically, a hybrid between the Air Coryell and Run and Shoot systems that revolves heavily around a two-tight end personnel package. Brady will call a play in the huddle, but the play he calls in the huddle might be completely different once they get to the line of scrimmage. When they approach the line of scrimmage, Brady diagnoses the coverage and has to determine who's blitzing, who's dropping. He then has to communicate to his offensive line the correct protection scheme. Then, based on the coverage, he has to communicate to his receivers what the proper route to run is, and trust that his receivers know what adjustments to make based on the coverage.
In the run and shoot, routes can basically change on every different coverage. Not just on hot routes, but just a route tree in general. It's a ton of information for a quarterback to process, and Brady has to communicate all of that information to the offense before the ball is snapped. He has complete control over the offensive huddle, with the latitude to change plays and audible and change almost every aspect of the offense on the field. Particularly in the no huddle, or the "sugar" huddle.
When Cassel was in the game, the offense the Patriots ran in 2008 didn't look much like the historic offense than was on the field in 2007. Oldfan asked if Brady is not tightly controlled. I say no, he's not. He references one instance in which Belichick informed Tom Brady (who was playing in his first game since coming back from his ACL and was getting a little "restless" in the pocket, shall we say) to set his feet and throw the ball as proof that Brady is tightly managed. The Patriots relied on a more run centric, play action based passing attack with Cassel, which featured Cassel rolling out and throwing a lot more screens (which is saying something, because the Pats are a pretty screen heavy team), with shorter, less complicated routes and less audibles.
The same can be said of Peyton Manning and how he ran the offense in Indy and how he's slowly adapting to the offense in Denver while he works in conjunction with Mike McCoy.
Grading on physical stats is a bad measurement because it ignores too many other factors. It removes applicable data to a quarterback's talent level to come to a conclusion that is easily disproved by the number of physical specimen's who straight up busted. Quarterbacks who are better athletes do technically allow an offensive coordinator to do more in an offensive scheme in terms of what routes you can run and that kind of thing, but if you don't have it between the ears, or your unwilling to stay in the pocket, it doesn't matter how good you are physically.
Michael Vick (at least until Robert came along) was the most physically gifted quarterback in the NFL. Pound for pound, in raw arm strength terms, he might have the best cannon in the game, and we all know how dangerous his legs are. But he still has a tendency to want to bail out of the pocket if a play takes too long to develop. In 2010, it seemed like he'd shaken then habit. In 2011, the habit came back. He leaves big plays on the field because he trusts his legs more than he trusts what he sees in the passing gain. So he may scramble and make a spectacular looking play based on his athletism, but he'll leave a potential touchdown on the field because he didn't want to hang with the play.
The same can be said of Cam Newton.
It can be stated that the systems and support systems around these two guys aren't the most stable at the moment (it was much more so in 2010 and 2011 than it is in 2012), but when you watch tape or watch the games and watch them critically instead of as a mere observer, as athletic as those two are, they leave the kinds of plays on the field that a Tom Brady or a Peyton or Eli Manning or Matt Schaub or Aaron Rodgers or Drew Brees can't and don't. None of those guys are the kind of athletes as Cam and Vick, and perhaps that forces them to focus more intensely on the passing game.
It's also hard to knock those quarterbacks for playing in more quarterback friendly systems when Carolina basically adopted Auburn's offense to make Cam comfortable and Vick is playing for Andy Reid, who allegedly has this great knack for designing a quarterback friendly pass offense that many quarterbacks like A.J Feeley and Jeff Garcia and Donovan McNabb and Kevin Kolb have flourished in. Someone like Cutler was locked into a stringent system under Martz where he couldn't audible or dictate his own plays. Now with Mike Tice and Jeremy Bates who has far more freedom and latitude, and yet he still makes the same sort of boneheaded decisions.
And now it looks like Blaine Gabbert, who was supposed to be the prototype for what athletic young quarterbacks should be, is going to be usurped for a job by Chad friggin' Henne.
Sometimes the problem with being more athletic, is that your whole life, you've been able to "out-athlete" someone. To get away with things that people who aren't the same kind of athlete you are. The hard lesson of the NFL is that you have to learn to get out of the mentality if you want to succeed. For the guys who aren't athletes, you have to make up for the lack of legs with the lack of arm with something else.
Physical traits are just a bad way of evaluating a quarterback's ability, unless you already have an idea in your head that those who are more athletic are always going to be better, regardless of how they perform on the field. Ultimately, how quarterbacks perform on the field is all that matters. The role of the quarterback in a team's success is indeed exaggerated, but it's important, and having a really, really good, smart quarterback, sometimes, is better than having the more athletic quarterback.
Luckily it seems like RG3 is both.