Idealistically, there would only be one softball league and women and men (straight and gay) would be able to play on any team they like against other teams that would accept any sex/orientation... but I'm sure someone would have a problem with that because the biological makeup of one sex may predispose them to be favored for certain spots on the team or all spots. (ie: imagine any WNBA team playing any NBA team... would women even be recruited for NBA teams?)
It should be noted that this only really applies at
really high levels of play. The physical differences between men and women (on average) are not that big. At lower levels of play, practice and hard work matter far, far more.
To answer your question, probably yes. Just not as often.
My view on it is this: Could not the same argument be made about other genetic traits that, on average, give an advantage? The most obvious is race. Depending on your genetic makeup, you might be taller than average. This obviously gives an advantage in sports such as basketball.
If you look at the USA's sports teams (such as basketball and american football), there's a very large amount of african americans. They do not however hold a monopoly on playing these sports competitively. Similarly, I do not think men would have a total monopoly on playing these sports were women included.
Another thing of note... does anyone really care about the WNBA? To me it seems like it is viewed as the "lesser" league. Why? Because any time you have more than one league, one is going to come out on top and be the "important" one for that sport. That women are not allowed to play in the "real" league does not sit well with me.