I have a performing group that does slapstick as part of their show. The guys are better than the girls, but I think it has a lot to do with their stage presence than anything. There’s one girl I’d love to get involved in our group but she lives too far away. She would be equally as funny but using different moves than the guy.
However, I do think you have a point… we have one move where the guy literally flips in the air and lands on his butt- I can’t see how that would be funny with a girl doing it. I think people still have that inherent “females=fragile” mentality and seeing a pretty girl flip midair/land on her butt would not be funny but (gasp!) Lucille was funny mostly because of her reactions and mishaps—I might be wrong, but did she ever do anything seriously physical, like fall out of the sky?
Slapstick, like most comedies, depend on the audience to understand the underlying humor, so the director has to ‘get’ the audience before being able to draw out their laughs.