Exactly my point.
China should have won 3 WCs by now. What's their population, billions and shit. Ditto for the money they have
American who lived in China for 5 years chiming in here.
China does not have much of a football culture to speak of. When you walk through their cities, you'll see plenty of basketball courts, but no soccer fields. They also don't have quality coaches to develop the players who are serious about the sport.
Football is unique from a lot of sports in that an individual needs to start playing at a very young age, and receive quality coaching during their development to reach the top of the sport. The populations of China and the US mean very little without that.
I'm from North Carolina, where basketball is king. Kinston, a small town in the eastern part of the state, has produced several NBA players because kids grow up playing the sport, and even their parents or youth team coaches know enough about the game to teach them solid fundamentals when they start playing. It's not a coincidence that many American stars (Pulisic, Bradley, etc) have parents who coach the game. Without that, it's very difficult to succeed.
To answer the original question, I think the US would be the best, but I don't think it would dominate, as football isnt a sport where it's easy to win consistently. They would be going deep in the world cup every 4 years, though. I think they would win 1 out of every 3 or 4 world cups.
The thing with American sports is that we have so many good athletes who go into basketball or American football, and even play at the college level, but don't make it in the top leagues. European basketball leagues are littered with American stars who couldn't make it in the NBA. If all of those kids were funneled into football and given proper coaching, plenty could become stars. Guys like Lebron James and Russell Westbrook might not have led the US to world cup glory, but it couldve been the guy who got a scholarship to college and nothing beyond that, but is still every bit the athlete that Christian Pulisic is.