Safer in terms of what?
Wallace is the better defender.
Wallace is the better post threat.
Heck, Wallace is the better guy to pull the other defender out of the paint.
And the one thing Williams does better, rebound, doesn't improve the team rebounding when he is out there. In fact, defensive rebounding drops by 5% when he is on the court.
He is the perverbial 3rd QB in the NFL. Never plays but the fans think he is a star.