"Both newspapers and scientific journals frequently state three facts about the Spanish flu: It infected 500 million people (nearly one-third of the world population at the time); it killed between 50 and 100 million people; and it had a case fatality rate of 2.5 percent"
The math here is off wildly. If it infected 500,000,000 people and had a case fatality rate of 2.5%, it would have killed 12,500,000 (which, you'll note, is lower than even the lowest estimate provided). If it infected 500 million people and killed between 50,000,000 and 100,000,000 people, it would have had a case fatality rate of between 10 and 20%
Both of these things cannot be true.
The confusion here is "case fatality rate" (Case fatality rate is calculated by dividing the number of deaths from a specified disease over a defined period of time by the number of individuals diagnosed with the disease during that time; the resulting ratio is then multiplied by 100 to yield a percentage*) with global mortality rate (...number of deaths serves as the numerator for both measures, mortality rate is calculated by dividing the number of deaths by the population at risk during a certain time frame.*)
The global mortality rate of Spanish Flu was between 1 and 6%, the case fatality rate was between 3.4% and 20%
The current global mortality rate of Covid-19 is 0.000126% (though, that will absolutely climb and the final number won't be known until the whole thing is over...). The current case fatality rate is ~4.15% (this number is obviously high because deaths are easy to count, while we don't have enough tests globally to accurately determine the number of cases)
*( https://www.britannica.com/science/case-fatality-rate )
Editing to add that while I did the math myself here, I read the Wired article that was quoted afterwards, and he actually did the same math as me and came to similar conclusions (he ruled out the extremes and came to this conclusion "we find that a reasonable estimate for the global case fatality rate of the Spanish flu is 6 to 8 percent. To be clear, this means that 6 to 8 percent of those who were infected died. Global mortality of the Spanish flu—which is to say, the proportion of all people everywhere (infected and uninfected alike) who died from the disease—was probably between 2 and 4 percent."). He also adds "Johns Hopkins University epidemiologist Jennifer Leigh recently told The Los Angeles Times that the overall [case] fatality rate for Spanish flu may have been closer to 10 percent."
This is why it's important to read the whole article, rather than cherry picking one line to back up your argument.