On the Spanish Flu specifically, the evidence indicates most people who died were killed by secondary bacterial infection, not the virus itself[1]. This was the result of a combination of poor hygienic conditions and lack of antibiotics. Considering that, I think what we are witnessing with SARS-CoV-2
is about what the Spanish Flu would look like today.
[1] https://academic.oup.com/jid/article/196/11/1717/886065