They say currently around 10% of the estimated total number of 5G base stations to cover countrywide installed. So it only works in Seoul, the capital city in Korea. They estimate 5G will cover the whole country in 2023.
FYI, because of its frequency characteristics, the cover range of a 5G station is much shorter than that of a 4G station, almost one-fourth of 4G. So much more base stations required than 4G.
The U.S. is also using 600mhz, 3100-3500mhz bands, which should have ranges equal to LTE. Though with lower switching costs, which should lead to fewer towers?
Base stations in dense cities may be reduced because of the decreased traffic per tower.
I'm not an expert but it won't have difference in that case I guess. The current Korea's 5G is deployed at 3.5GHz whereas 4G is usually at 1.8GHz in Korea, so it would have shorter ranges or the technologies is not mature yet. The articles describing the current 5G deployments are a mess so I'm not sure.
However, 5G won't have any significant advantage over 4G in those frequencies other than a little bit improved throughput. The ultimate goal of 5G is to use frequencies above 6GHz, usually around 28GHz (!) in order to have sub-1ms latencies and ultrafast throughput. This requires numerous "small cells" deployed.
I found unbiased sources below. You will find that these articles assumes the frequency above 6GHz should be used.
