For Harding, it was the scandals that caused his historical rankings to fall drastically. One of the most infamous scandal, which was also compared to the Watergate scandal, was the Teapot Dome scandal of the early 1920s surrounding the secret leasing(bribery) of federal oil reserves by the secretary of the interior, Albert Bacon Fall.

As for Calvin Coolidge, some people criticized him for his laissez-faire attitude, meaning that the government did not intervened with the affairs of companies.

For Hoover, it was just the time period, he tried to solve the issues that the great depression caused but unemployment rate still continued to rise. Can't really blame him, the world was also suffering and it was a huge task to try to the the economy going.

As for FDR to Eisenhower, I feel that their success was partially due to the time period, WW2, Korean War and the Cold War. FDR helped the US to get out of the economic depression. Overall, the three presidents were seen as hardworking and had accountability, thus ranking decently in the rankings.

To judge a "good" or a "bad" president, it would be good if we have the benefit of hindsight so that we can effectively judge the decision and policies introduced by them. With hindsight, we would probably be able to see the long term and short term effects of these policies. However, without hindsight, it would be really hard to gauge how "good" a president is. We can only judge by the reasoning of his policies, the immediate changes these policies causes and how much accountability his cabinet has.