Heinsberg study suggests a mortality rate of about 0.36%. This is high, but not "a big threat". Given that with 0.36% and 15% infection spread in the general population (like flu) you look at ca 162k deaths in the US.

It is not even close 5.7% mortality. If it would be that lethal you would look already at over one million deaths.

Sweden is a good example of a country without a lot of counter measures and we see that it will end in the realm of 0.36% lethality (5,4k deaths). https://en.wikipedia.org/wiki/COVID-19_pandemic_in_Sweden