You're right, Tom Brady is an enigma that will never happen again.  Even Joe Montana was a 3rd round pick.  The only thing that comes close to Brady might be Kurt Warner who was undrafted, but you don't find hall of fame QB's in the 6th or 7th round generally speaking.  Siemian very much reminds me of Brian Griese where he just didn't have the physical tools to be an NFL QB but he was very likeable and a smart guy, so he had a ton of defenders around him.  Under no circumstances do I think Osweiler is the QB of the future, but he has a much better arm than Siemian and some scrambling ability that I think will take some pressure off the o-line and stop teams from stacking the box.