Let me remind you of your words:
Anyway, Bethel was a terrific returner in '03, but his numbers dropped precipitously thereafter (from 28 YPR in '03 all the way down to 22 YPR in '05). As for ST tackles, I don't think that's generally what you're looking for from a 2nd round WR.
Bottom line, he was a bust who likely would've been cut, and the Pats got a former 1st rounder for him. If Sullivan busts, the Pats don't lose - they're simply back to even.
In any event, it's moot, because Bethel DIDN'T make the roster (he was traded), while Sullivan still stands a chance to.