I know little about Nick Williams actually but he has looked fine defensively out there while Vaughn is still learning. I am not arguing for Williams...all I am saying is that you do take a risk sacrificing defense for potential offensive output....see 2006 CF.
I am trying to remember what game it was that a ball landed close to the line in LF and the announcers clearly said a seasoned LF would have had it when Vaughn could not get to it. Was that part of that awful inning in Seattle or a different game?