The USA has the 10th-fastest internet in the world (source: https://www.fastmetrics.com/internet-connection-speed-by-country.php, scroll down to the 2017 update), beating out most of Europe (the only European countries ahead of the US are Switzerland or Scandinavian).
I think you may have been mislead about America's internet. But yeah, South Africa's is pretty lousy.
It's still probably better than you'll get with Starlink, though. When it comes to cities, there's two reasons Starlink probably won't catch on:
In many cities, existing internet speeds are going to be faster.
Even in cities where that isn't true, Starlink doesn't have the bandwidth to serve a major metropolitan area.