PROSPECT = what you observe of him before the Draft, not after
David Carr was the best QB I've ever seen play college football. Many of his throws 30 yards plus down the field were "hitting the Frisbee," meaning if you stood next to him and threw a Frisbee 30 yards, he'd hit it with his throw. Quick release, excellent decisions, Elway arm, seemed to be a high character leader type.
The Texans acquired Tony Boselli to be their OLT. He never played a down for them, shoulder. Their OL was an absolute disaster and that was one of the saddest destructions of a QB ever recorded. David Carr was destroyed physically.
So, yeah, greatest ever prospect = destroyed in NFL with horrible OL play