LeBron mighta been a hell of a centre-half, though.
The top NBA and NFL players wouldn't necessarily be populating our national team (or even MLS) if soccer were the king sport in the US. However, you have a ton of young athletes with bodies suited for soccer who never played it seriously, and instead get scholarships as point guards, cornerbacks, etc.
As to athleticism of the current team, they're very fit. But with a larger pool to draw from you'd presumably have some equally fit players with actual skills to boot. To get that pool of talent the US will probably need better high-end youth programs and just more interest. It's a cliche to say soccer's a "street sport" everywhere but here, but it's true. Adolescent boys don't obsess over soccer as much as they do other sports, or at least they haven't in the past.
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*and German youth squads
