The mass testing is a double edged sword though. Yes, all those "positives, but mild cases" keeps the mortality rate down. But all the testing gets those positives "off the streets" faster. Which also keeps the mortality rate down because those people aren't going to visit their "high risk" family members, or going to their jobs where they interact with "high risk" customers. That is something that isn't happening in the US, and there will be consequences.
The places I am keeping my ear out for are the assisted living communities, senior centers, care centers etc, since those are where the fatalities will occur. My concern, is that we are still in the early phase and so those consequences of younger, healthier, but positive individuals interacting with the high risk population haven't been felt yet. And since we have inadequate testing, we have no idea when that time bomb is going to explode and if our hospitals and necessary equipment will be able to cope with it. The problem Italy is now facing.
So I don't really see how South Korea's low mortality rate really helps us predict anything when we have likely many "positive but asymptomatic or mild cases" interacting with the 70 million people in the US that are over the age of 60 when we aren't taking the same steps to control the spread.