Arsenal's Williamson, who did not feature in the four-team tournament until the final group game, said every player would have an important role as England look to build on their third-placed finish in 2015 and win a first World Cup title.
"We call ourselves The Finishers. We're not The Bench, we're there to back up anything that's going on the pitch and have a positive impact," Williamson was quoted as saying by the Guardian newspaper.
"There's people that are going to go to a major tournament and not be involved, and that's a reality and part of being a footballer. We work really hard on the team.
"It's a hard balance to get when you go away for a tournament, hopefully for the longest time. The fact that we've shown that those players can come and deliver when they need to is important."
England, who are fourth in the world rankings, have been drawn in Group D alongside Scotland, Argentina and Japan at the World Cup. They open their campaign against Scotland on June 9.
(Reporting by Shrivathsa Sridhar in Bengaluru; editing by Sudipto Ganguly)
