all of its young children were dreaming of representing the US at the World Cup, as is the case for most countries. It's not about "if Steph Curry and Lamar Jackson played soccer" it's more about if tens of thousands of children who devote their youth to basketball and football and baseball instead devoted it to soccer.
Being an elite athlete in multiple sports is so uncommon it does nothing for this argument. But out of the countless kids who are good enough to play other sports at the high school or college level, there's likely enough to field a full team of elite soccer players if they all grew up kicking a ball around instead.