A World Cup Simulator is most useful when it gives you a fast first draft, not a final answer. This World Cup Simulator can run balanced, favorites, and upset paths, then let you open the bracket and adjust anything that feels wrong. The point of a World Cup Simulator is to start the conversation with a believable route.
Use the World Cup Simulator when you do not want to enter 72 group scores one by one. Run the World Cup Simulator once for a baseline, run it again for a different path, and compare the champion, group winners, and final route before you settle on your own prediction.