Separation in college does not guarantee separation in the NFL. The NFL has bigger, stronger, quicker, faster and more talented players. Polk ran a pedestrian 4.52s 40 and declined to participate in the 7 cone and shuttle (very telling).
During OTAs he looked slow to me, but I am not an NFL evaluator. Still, I have not seen a quote from any NFL commentator (former scout, player, or coach) saying that Polk was getting good separation during OTAs or minicamp. If you have some, I would like to see them, because I looked and found none.