And actually, Brady was a 6th round pick in only his second year.
Just because you are picked in a later round doesn't mean you don't have what it takes. Terrell Davis of the Broncos was also a 6th round pick. They also had an 11th rounder by the name of Karl Mecklenberg that became All-pro. Joe Montana was a 3rd round selection the same year they took Dwight Clarke in the 10th. I might add that they finished with the worst record in the league in the prior year and were winning the Super Bowl 2 years later. Jake DelHomme was an undrafted free agent. Kurt Warner was another undrafted free agent who actually backed up Banks behind Steve Bono when they were all with the Rams.
First round flops are plenty: Ryan Leaf, Tim Couch, Tony Mandarich, Ki-Jana Carter, Art Schlichter, Heath Shuler, Kelly Stouffer, Blair Thomas, Lawrence Phillips, Rick Mirer, Rashaan Salaam, etc.
At some point somebody just has to determine that the later round selection deserves a chance, especially when the high-priced 1st rounder isn't producing and is going to cost a lot of money to keep around. These are just plain examples.