"it's plausible that more than half of the population could get it, and leaders of many western countries have acknowledged that."
Will there ever be apologies for spreading mass hysteria?
E.g. in a recent turnabout Vice President Mike Pence said today that there has been “irresponsible rhetoric” from people who have downplayed the seriousness of the U.S. coronavirus outbreak.
Edit: also pneumonia is caused by a large number of causes. If covid-19 killed as much as all respiratory diseases it would already be scary.
The numbers don't need any mitigating factors but those do exist as well. I don't see South Korea doing anything more extreme than what could be done in the US so that doesn't show the US would be worse. The population density of South Korea is 15x that of the US so that would probably mean the infection rate would be lower in the US. The median age is also higher in South Korea and since this disease affects older people more that would also make the outlook for America better.