Indeed, they are the leaders of most fields for now, maybe except for Table Tennis
But America only became a superpower after the Second World War, when the other nations were wrecked while they remained relatively unharmed
Before it attained superpower status, it went through a lot of turbulence before it is where it is now.
After the independence in 1776, America fought against the British again in 1812, suffered a devastating civil war that nearly took the U out of USA and then fought with the Mexicans in their border wars. Even when they opened their borders to immigrants, there were lots of social problems, not forgetting the ongoing war between the settlers and the red Indians. The Irish came in droves and they were a source of social problem with their own enclaves and gangs. Then the Italians which need no further explanation regarding their mafia. Of course, not forgetting the blacks who toiled in America but their presence remained a source of friction and still segregated by the whites back then.
Even in the 19th and early 20th century, many homogenous European nations were ahead of America. The British had their powerful navy and numerous colonies, the French with their North African colonies, the Dutch with the East Indies. In fact, back then, America was besieged with social problems and stood out little. America was considered the sick man among the whites.
When World War II broke out, the Americans were rotundly trashed by the Germans in their first few battles in North Africa (Kasserine Pass) whereas the British managed to stall the Germans despite their lesser numbers. It was well known that the British army was far superior in tactics and plans compared to the Americans, who were still using First World War weapons and tactics. Even the American guns were considered antique to what the Germans were carrying and their planes obsolete compared to the Japanese zero fighters. It was only after America managed to poach the Germans and Japanese bright minds that kickstarted their rise to the top.
My point is that it is always the homogenous nations that will always have the upper hand as they do not suffer from social issues or a divided demography. Singapore is still ironing out the social issues, now worsened by the influx of FTs. The problem is also that our education system discourages critical thinking and we are unable to poach the talents from other nations, only the charlatans