Absolutely true. Boxing is a great example, because the heavyweight division is (or always was) considered to be an “open division,” meaning that those in lower weight classes could fight as heavyweights (which happened occasionally). Of course, a heavyweight could not fight in a lower division, and no sanctioning body would ever allow, say, a junior flyweight to fight a middleweight, let alone a heavyweight. In other sports, like golf, there is no prohibition on women competing against men, but the opposite would never be allowed in an official event. Let these poor souls have there own division, and see if anyone would pay to see it.