Like for example, Justin Blackmon was a 3-star, #91 rated WR, and JJ Watt was a 2-star, not even ranked DE.

And plenty enough of the 5-stars flame out, whether they suck in college or just aren't good enough to make the league (like a John David Booty, a fine college player but just not good enough for the NFL).

But there's also only around 40 5-star players, 200 or so 4 star players, and way more 3-star players. It's more of a probability than anything for certain. Just like picking in the draft, if you have a top-10 draft pick your chances of getting someone good is way higher, but that doesn't tell you if any individual player will be good, and some guy you pick in the 2nd round could still be a star.