The worst part is that Kaido fans have been hearing for years that Kaido was a fraud from people who are fans of Garp. Kaido has never been proven to be a fraud, while Garp's greatest achievement is explicitly shown as a fraud by Oda.
See how the world turns.
1º - In the very chapter, it is shown as a fraud because Sengoku says that Garp received help from Roger.
2nd - Oda brought 123,123 people to the island to make the defeat of the Rocks Pirates more credible and to show that it wasn't just Garp and Roger alone.