Williams just doesn't have the skill set to be an every down player at the moment. May be he can develope pass rushing skills as time goes on, but he shouldn't be out there in 3rd and long situations because he doesn't provide pressure.
Pierce has a chance to learn and may be evolve into what we hoped Jernigan would turn out to be. But now, as our only inside threat, he will probably now see the G/C double team. He will have to learn to evolve his pass rushing skills now that he won't be 1 on 1