Does NFL Rely too Heavily on Combine Numbers?

With the NFL combine being held now, does the NFL rely too much on the performances the players put on during the workouts rather than the performance on the field? Maurice Clarett put up very impressive numbers his freshman year on the football field. Even after being out of football for a few years, he was expected to be drafted in the third round of the draft. After his numbers that he put up on Saturday with a 4.72 and a 4.82 seconds forty yard dash times and quitting on the rest of the drills, many critics say he might not even get drafted because of such a poor performance this weekend. So my question is that do NFL teams rely on the combine numbers too much?