Ten other teams didn't pick him as well, which means that 1/3 of the NFL passed on him. He's easily as good, if not better, than any of the guys picked before him (Mario Williams is debatable). And as you said, there's no sure thing, so playing hindsight with this is pointless, right? I'm sure there are loads of players you wanted who were busts, and the fact that there are ANY 1st round busts indicates that drafting isn't an exact science. Which is the point.
Again, this goes back to the "inexact science" thing. And it's a little easier to project how a player will do on your team after you've seen them against real NFL compeition, than seeing what they've done against mostly non-NFL competition (in college).