True. Males have XY sex chromosomes while females have XX sex chromosomes; the male can contribute the X or Y chromosome, while the female must contribute one of their X chromosomes. A male infant results if the male contributes his Y chromosome while a female infant results if he contributes his X chromosome.
However, sperm have to reach the female egg, if the path for sperm Y is good, then the child will be male, right ??
Of course, one may argue that, if the men produce more Y sperms and then they will have more chance to conceive a son. But that doesn't mean there is no chance of getting a girl, even if the man produce more Y sperm. Which sperm able to reach the egg is the hero.
Assume the terrain is bad. Then it doesn't matter whether there are Y sperms are strong or not, no child will be conceived as no one can reach the egg.