There are plenty of talented gymnasts from all over the world, and plenty of them can win a gold medal in 2020. It's not like Simone Biles is going to dominate the sport forever. That said, we have a large athlete pool with lots of time and money to spend on training, so the USA does have an advantage.
Simone Biles is the best gymnast I have ever seen and I have been watching gymnastics since Olga Corbutt. The other girls on the American team are powerful and in a league by themselves also. Their domination in the sport has never been seen before. There are no other countries who even come close to giving them competition.
In the 1980's the USSR was a big rival for the US in gymnastics, but since the fall of the Soviet empire there has been no other country that has the resources and athletes that could be a rival to the US in this sport, especially with powerhouses like Simone Biles.
The US women, even outside of Biles were the second and third best gymnasts at qualifying. So our second and third best women achieved higher scores than the best of the rest of the world. US dominance is why Gabby Douglas couldn't compete in the all-around competition, and why they're going to 4 person squads in the next Olympics.