I think people are being overly harsh on Williams and possibly also Ramsay. They aren't the most technically gifted players, that's for sure, but off the ball, along with Dugandzic, they play a very important role, drawing defenders away, and creating space for Engelaar and later Kewell to dictate the game. Their pressure when we don't have the ball is very good as well. Just out of interest, I compared Williams and Troisi, and while their attacking stats are actually very similar, Williams' defensive stats (tackles, interceptions etc) far outshine Troisi's. Defence starts from the top, and I think one of the most important parts of the team's resurgence has been the defensive pressure that for the most part simply wasn't there.
Ideally Williams would be better off as an impact sub, but for now, he should keep his spot in the team.