I think the argument still applies on a shorter timescale. The child mortality rate in the US fell from 26 per thousand in 1970 to 7 in 2020 [1]. It seems reasonable that some portion of kids that now have treatable but persistent illnesses such as allergies/asthma would have died just a few decades ago.

[1] https://www.statista.com/statistics/1041693/united-states-al...