But why is it more useful to call every imaginable developmental anomaly a separate sex? If we do that, does sex even mean anything? Definitions are as good as useful the resulting categories are. If you can’t even begin listing the biological sexes that you think we have to consider, what on earth will anyone ever be able to use those categories for? Yes, saying there are males and females is useful categorization of not just humans but many animals, because it captures a pretty significant dimension of individual variability arising from separate developmental programs. The existence of exceptions doesn’t render it useless, you can say “I have male chromosomes but my body developed like a female would “ without requiring a biological sex category covering your specific case.
Edit: btw this is not the area of genetics and Y is a chromosome not a gene.