Other than not turning a post-war recession into something worse, what did he do?
You think prosperity is worse than recession??
Underrated means that is wasnt as bad as is commonly said. Harding is commonly listed at the bottom, so it shouldn't take much to make him underrated.
He brought peace, freedom & prosperity after the war, repression, recession & riots of Wilson.
He ended Wilson's segregation of federal offices & supporting anti-lynching legislation
He reduced taxes and reducing the government control of businesses instituted in the Wilson years
He pushed through the Budget & Accounting Act which created the more systematic federal budgeting system we are accustomed to today.
He brought about the Washington Naval Agreement which was an impressive naval arms control agreement. He signed peace treaties with Germany and Austria, which replaced Wlson's failed Treaty of Versailles. He dealt successfully with Labor and Business regarding strikes and work conditions in the steel industry. He established the VA
He made some strong Cabinet choices -- Hughes, Hoover, Mellon, Wallace, Davis, Weeks; but also some bad ones -- Denby, Fall, Daugherty.