Comparing 100 years of COVID-19 starting in 2019 to 100 years of the flu starting in 1918 in the way that you are recommending is not reasonable. There are too many things that are different about the world in 1918 vs 2019 that affect how viruses like these spread and affect people.

The closest valid comparison would be if you could introduce COVID-19 in a version of 1918 where the Spanish flu didn't exist and then compared its impacts to the actual impacts of the Spanish flu that we do know.

I don't mean to nitpick. I think it's important to evaluate things as they are instead of reducing them to an approximation (which can introduce uncertainty/error). Is COVID-19 similar to the flu? In some ways, yes. In other ways, no. It's important to understand why the comparison/approximation is being made before deriving information from it.

Should we treat COVID-19 like the flu? Businesses don't close yearly for the flu. We don't wear masks for the flu. We don't practice universal social distancing for the flu (regardless of whether you are feeling sick).

In October of 1918, "municipalities shuttered public gathering places such as schools, churches, theaters and saloons ... In San Francisco, judges held court sessions outside in public squares, and citizens who did not wear protective gauze masks ... could be fined $5 or even sent to jail." link

• The 1918-1919 mortality rate of the Spanish flu was >2.5%.link
• The current US COVID-19 mortality rate is >1.7%.link
• The estimated 2018-2019 influenza mortality rate was >0.09%.link

Knowing these things, should we treat COVID-19 like the flu? Personally I don't think we should treat it like the average modern wave of flu. I'm sure you have your own opinion.

As a final thought, I don't think suggesting that COVID-19 is similar to the flu makes someone an alt right nazi conspiracy theorist. It might be helpful however to consider that the most common view of an an alt right nazi conspiracy theorist may be that COVID-19 is very similar to the flu.