Still.
You have countries like England, Brazil, Italy, Argentina, France, Spain, Germany, Netherlands etc etc, all with huuuuuuge domestic leagues and highly competitive regional tournaments, huge budget for said leagues and national teams, all generating the most highly valued players every year, each of those countries loving football even more than America loves the Superbowl, and none of them have it "easy" when competing for the WC.
So I don't think a hypothetical USA team could easily win a WC especially if you remember that they struggle with their sports that are already popular such as Baseball, Basketball and American Football against other countries.
Could the become more competitive given more resources? Of course, and they're doing so slowly but surely, 10 years ago they weren't even considered for anything, now big teams watch out for them.