Not only are first round pick QBs not guaranteed to succeed, the odds are strongly against it. Even if you limit it to top 10 first round picks, the success rate is pretty horrible. Over the last 15 years, 20 QBs have been taken in the top 10. Five have been good: Manning, McNair, Bledsoe, NcNabb and Vick. Four could be considered mediocre at best: KCollins, Jeff George, CPalmer and BLeftwich. Two are two early to tell, but did nothing impressive last year: Mannign and Rivers. The other nine were horrific failures: Akili Smith, Ryan Leaf, Heath Shuler, Rick Mirer, David Klingler, Andre Ware, Trent Dilfer (well, maybe just sub-mediocre), Tim Couch and Joey Harrington (maybe too early to say horrific).
In other words, the "success" rate is about 25%, with a 25% chance of a mediocre Jay Fiedler/AJ Feeley quality QB, and about a 50% chance of a complete abortion. And again, that's looking at top 10 picks. If you go further down, you start to include the Jim Druckenmillers, Dan McGwires, Cade McNowns . . . . hey, wait a minute, didn't all of these guys have a cup of coffee with the Dolphins? As much as we like to grouse about John Avery, Eric Kumerow, Billy Milner, etc., none of those guys can hold a candle to Leaf, ASmith, Shuler, Klinger or Ware as collossal draft busts.
If the guy isn't "special," don't waste a 1st round pick on him, or even a 2nd. Once you exclude the special guys, you can get adequate guys without spending the picks. In my view, Manning, McNabb, Brady, Culpepper and Favre are special. After that, you're looking at a fairly large group of guys that can succeed in the right system with the right talent around him, but are also capable of stinking up the joint if the conditions aren't right. Think about all the QBs over the years that have had one or two Pro Bowl years amidst a career of extreme mediocrity (or worse): Gus (1997), Jeff Blake, Kerry Collins, Trent Dilfer, Doug Flutie, Brian Griese, Brad Johnson, Testaverde, Rich Gannon, Trent Green, Ken O'Brien, Mark Rypien, Bobby Hebert, Jeff Hostetler, Steve Bono, Chris Chandler, Steve Buerlein, Elvis Grbac, Kordell Stewart, Jay Schroaeder, Wade Wilson, Dave Krieg, Don Majkowski . . .
One of the biggest problems with investing a high draft pick in a QB is that you have to pay through the nose for them, thus tying yourself up under the cap for years to come. You also feel committed to going with them even if it becomes clear early on that they are not the answer. In the meantime, you have a bad QB and a bad team.