I don't think it was a very fair comparison to use Jamaal's first two seasons and Brown's last two. Though even then, Jamaal's was still similar or better.
The edge is with receiving and that's it. But it's not like Williams is a bad receiver. He was 2nd on the team as a freshman and hasn't had QBs use him like the other QBs used their guys. If he got the 35 receptions that he should get, it would be a little different. No matter what, Brown is still a better receiver, but when you add it all up, it's obvious who the better overall RB is.

He's done much better against better competition, in shorter time, yet with a worse supporting cast, and arguably worse choice of play calling for him.