^This.
It's not a unique rosterbation concept. But in reality, the return is less than the pick originally expended. The only way it turns out is if you are looking at 7th round/UDFAs. Unhyped backups with no tangible record are rarely worth more than 6th round picks.
Don't think for a second that another team is going to give up a 3rd round pick and swap places in the 2nd round for your unproven 3rd round pick. That simply never happens in a million.... ok well maybe just ONCE.
The other problem too, is that we just remember the Matt Hasselbecks and the Mark Brunell successes. I'd agree that Green Bay is the model franchise for developing prospects. Here is the complete list of QBs they've selected since they picked Aaron Rodgers in the first round:
1. 2005 Rodgers (24)
2. 2006 Ingle Martin (148) out of the league, no value
3. 2008 Brian Brohm (56) Cut, signed off it's practice squad by Buffalo. No picks of any kind. No value
4. 2008 Matt Flynn (209) Signed as UDFA. Partially resulted in compensatory pick (#167). Loss of Scott Wells is the more dominant factor as it's predominantly based on playing time, with secondary emphasis on salary.
5. 2012 BJ Coleman (243) out of the league, no value
So if Green Bay is the model/best team to develop QBs for picks, then in essence they traded:
Give:
2006 5th
2008 2nd
2008 7th
2012 7th
Receive:
2013 5th round pick.
That's way more than we spent to get Percy Harvin.
It is a fantasy to think you can cull QBs and turn them into picks. The reality is, teams don't trade for backups often. Even the good teams go through several anonymous failed attempts before they turn over a prospect that outside fans might remember. We simply don't pay close enough attention to the failures and never account for them. But if that's something you are proposing, then you have to account for the wasted picks too. And when you do you can see it's just a complete and utter waste of time.
Read the second link on Brohm. Obviously in 2008, GB fans were thinking the exact same thing. And it turned out to be fools gold in the end. It's not a new concept. But it's wiser to learn from other people's past mistakes than to learn them on your own the hard way.