I look forward to your citation disputing the truth of what he lays out in that paper. In the meantime, feel free to peruse the list here of people affirming the same stance:
https://projectnettie.wordpress.com/
Or someone else:
https://www.nas.org/academic-questions/33/2/in-humans-sex-is...
You should ask the people you run with why no human is born with a body not organized around the production of gametes. You'll notice that when you read about conditions like anorchia or ovarian agenesis, the sex of the person with that condition is not a mystery, it's literally in the name.
Biology is messy indeed, and that's why finding such a universal definition was so useful.