That exact argument, as witnessed in this here thread, cuts both ways. You are sadly right though that soccer at the pro-level will never rival the traditional American pro-sports. Which is incredibly sad as North America is not only the last great untapped Continent for soceer. But could well be the biggest of them all if anyone could crack it.
Save for maybe a hockey player, there's NO fitter athlete than a professional soccer player. If football players had to endure the same, non-stop physical exertion's on a Sunday it would literally kill the majority of them.