From 2013, Mike Glennon (3rd round) outperformed E.J.Manuel (1st) and Geno Smith (2nd) this past season. 2012 draftees Russell Wilson (3rd round) and Nick Foles (3rd round) were only two QBs with 100+ passer rating from that class. None of Luck, Griffin, Tannehill, Weeden, taken in round 1 made it into the 90s. From 2011 class, second rounders Dalton and Kaepernick finished ahead of all the first rounders, Newton, Locker, Gabbert, and Ponder, in passer rating in 2013. Sam Bradford from 2010 is hanging in there, but the other first rounder Tebow is out of football. Going further back it's hit and miss, Matt Stafford has put up some big numbers but the Lions are still in a rut five years later. Matt Ryan same with Atlanta after six years. Mark Sanchez is hanging on by a thread after his career started out promising. Then it gets real ugly with J. Russell and Vince Young further back.
Plus you take yourself off the QB market for a few years. Either in terms of using another high draft pick at the position or acquiring a promising young prospect through free agency or trade.