The most accurate response to how Sinclair Lewis differed from other Lost Generation authors like F. Scott Fitzgerald and Ernest Hemingway is: Lewis’ writing was influenced more by the previous generation's progressive ideas.
While Lewis did achieve commercial success and receive recognition for his work, he notably wrote about the social issues of contemporary American life and critiqued aspects of American culture, which aligned with earlier progressive movements. In contrast, Fitzgerald and Hemingway often explored themes of disillusionment and the search for meaning in a post-war world, stemming from their experiences as expatriates and their personal histories.