As far as Williams' place among the top tier PGs, I would rank him inside the top five. Below Rose, Rondo, Parker. Above Westbrook, Nash.
It may be a bit of bias on my part, because Rondo is one of my favorite players, but I think he is the best pure PG in the league right now, with the ability to put up some points, grab boards, but mostly because of his ability to get other players good looks. Parker is probably second, though.
Westbrook is a better pure scorer, but I think he is one of the most overrated players in the game today. I would take Rose over Westbrook in a heartbeat, maybe even quicker.