I'm sorry, but that is absolutely untrue. There's a reason they don't have male vs. female basketball, or softball, or tennis, or soccer (futbal), or American Football, or rugby, or hockey.....or pretty much anything. It's because human males, by nature, are built specifically to be (on average) physically bigger, more powerful, and more athletic, because they are intended by nature to be the hunters, the fighters and protectors of the group. Women can be great athletes, some of the very best in the world. But no, it is not "negligible" at all. There is a stark difference in the raw speed, strength, size, etc. etc. of most of the TOP male athletes in any given sport in the world, vs. the TOP female athletes in the world. And that is not, in any way shape or form a knock on women. That's just Nature, it's scientific fact. Men are on average bigger and stronger. Women were not built by nature to be hunters, fighters and protectors, so of coure men are (in general) going to have an advnatage over them in athletics.
That does not mean that there aren't some women who could compete or excel in male sports leauges. But what it does mean, is that they would be at a severe disadvantage in almost every sport. Could you imagine even the very best WNBA player competing in the NBA? If she's a great shot, sure. But in spite of the increasing amount of fouls, the NBA is a physical league, and a woman playing against 6'6"-7'0"+ men, just would not work out that great in the end. That is why they have a women's league in the first place. Could you imagine a woman trying to be anything but a kicker or punter in the NFL? Playing any other position, needing size, strength, speed and power, not to mention big athletic men being naturally built to absorb more physcial punishment......a woman would not last in the NFL, most likely.
It's not a matter of sexism whatsoever. It's simple science. There are women leagues because it evens the odds, and makes sports what they should always be: fair. And if you have a trans, who spent most of their life a natural born male, and they use cosmetic surgery and hormones to try and become female, that does not change or negate the fact that they were born a man, and are built like a man. As an athlete, they are going to have a physical advantage of some discernable sort over natural born female players. And that honestly isn't right or fair.