You can't measure this stuff in a vacuum. Take fifth round pick Justin Shorter: The following four receivers were more highly touted going into the draft than Shorter. If all of them went on to big NFL succcess, and Shorter did not, it would be fair to say Beane made a meaningful mistake. If Shorter and all the WR's picked after him fail in the NFL, one might complain it was a bad positional pick, but hard to complain more than that.
21) Parker Washington, Penn State
Round 6, Pick 185 | Jaguars
22) Kayshon Boutte, LSU
Round 6, Pick 187 | Patriots
23) Trey Palmer, Nebraska
Round 6, Pick 191 | Buccaneers
24) A.T. Perry, Wake Forest
Round 6, Pick 195 | Saints