Standing at a borderline 5'10", size is obviously the first detriment to the Florida corner's game. It would not be worth a mention if it did not hamper him, but as a 2014 game against Alabama's Amari Cooper showed, it can rear it's ugly head in the red zone, where contested situations are prevalent. Cooper blatantly got the best of him at two opportunities in that game.
Coupled with the lack of height comes the lack of arm length. Hargreaves is in fact strong, but his lack of arm length usually makes him the reactor in press situations, giving the early edge to the opposing wide receiver. While his feet are ridiculiously quick, if Hargreaves fails to cut off the receiver early in the route, he finds himself fighting against the odds, as shown against Alabama's Calvin Ridley on the first play of this year's SEC chapionship game.
When the quick feet fail, it should be up to the recovery speed and the natural athleticism to take over and cover for his mistakes. Jalen Ramsey consistently showcases it. Hargreaves however, does not. The 4.5 combine time matches up with the tape. Both Ridley and fellow Alabama alum Ardarious Stewart got the better of him on deep balls.
It is to be noted that cornerbacks his size have succeeded in the NFL. Jason Verett, Darrelle Revis and Asante Samuel are all sub 5'11" cornerbacks who have played at elite levels at some point in their careers with Verett (when healthy) playing it in this very day. One thing they all have in common, that Hargreaves does not, is sub 4.40 speed.
Cornerback is the position where athletics and thus combine testing has the most direct impact on ones game. Bearing that fact in mind, Hargreaves is closer to Brent Grimes then he is to Revis.
So how high should Brent Grimes be drafted? His best years were great, but he was always had to fight his size and speed defencies and was limited to off-man and zone to mask them.