"Europe" contains both Switzerland and Albania. Trying to average everything out across such a wide economic spectrum is meaningless.

I don't think it's meaningless on this context. Even the lower level of the average developer income in Europe would qualify. It shows the visa requirements are quite inclusive.

The US average salary is also lower than a California or New York resident but that doesn't mean the metric is bad. It simply means that ~50% of remote workers in America can move to Korea. Unfortunately, that also means ~50% of people can't. The same goes for Europe.