You're comparing absolute numbers. What about as a % of population?

World population is also up from ~1.8 to 7 billion which seems relevant for your comparison.

Different diseases, different population sizes/densities, different world environment, different healthcare capabilities. I'm pretty sure there's no way to say with any confidence that had most people just been forced to get on with their lives, fatalities would have been X% worse (assuming an otherwise equivalent outbreak in 1997).

and bear in mind there was no supplemental oxygen in 1918.