those elite football players would have been better than the current crop of elite American soccer players. What you are referring to is the potential for a broader interest and participant pool, and INCREASED MAINSTREAM CULTURAL RELEVANCE, which would help propel the improvement in quality player development because the general cultural status would then lift all boats. Essentially to the point where this statement, which is true for other elite soccer nations, would be true for us as well:
Soccer would marinate our entire culture.
On the latter interpretation you are correct. But let's be clear, this is NOT the same thing as the inaccurate "we are not elite at soccer because our best athletes choose football and basketball". Christian Pulisic is more "best" even in terms of potential in soccer than JJ Watt and Ziggy Ansah.