I have horses.
I have bred & foaled 6 of them.
I knew instantly at time of foaling what SEX each of them was.
NONE of them CHANGED their sex—except one colt that I gelded when he decided he was in charge. He made a very nice gelding after that “brain surgery” as we call it.
Even that one colt didn’t change sex…
LOL!!!
Well, we changed the gender of at least eight or ten of our horses. They had no choice in the matter, though.
Then, we competed them against mares and “real” males. There was never any controversy about “advantage.”
Even then, your horse was still male - he was just a gelded male.