Flattening other infectious disease curves has been proven to reduce total number infected.

STDs (GC/Chla/HIV/Trich): By flattening the curve we also reduce the total infected because the opportunities for infection are greatly decreased when there is far fewer infectious people out there.

Influenza: Airborne droplet, The more we flatten the curve, the less infected until warmer weather, Covid-19 may have a similar weather effect.

Polio: Before vaccines, by identifaying the cause of transmission of polio, and the fact that Polio was growing faster and faster every year as America became more urban, led to more infections as spread in urban children were higher risk for infection and increased spread compared to the children who grew up in the country and small town counterparts. By flattening the curve we gave science more time to find an adequate cure, because for decades they were treating these kids with Vit C and Quinine which proved ineffective. While no one knows how many lives were saved, most people agree that flattening the curve with quarantining saved tens of throusands of lives.

COVID-19 may be different than other infectious disease processes, but by flattening the curve typically you will reduce the chances of getting the disease, and eventually science will find a true breakthrough cure in most cases.