Here are some facts.
Intersex isn't tracked worldwide, but Kenya has done a census that found 1.7% were intersex. Intersex appears to be more common in Africa and parts of India than other ethnic groups.
High T is only banned in the 400-mile because the database of elite performances by intersex athletes was too small to show an advantage at other distances. (Note: This is most likely because a few intersex athletes who wouldn't have been good enough to compete at the world level probably show up in this smaller database. Their intersex advantage elevated them to national level but not to world class level so their performances weren't great.) I hope that was clear enough, but here it is another way. Just being intersex doesn't mean someone will be great. It just means they will be better than they would have been without the extra T. In a small database, a few mediocre high-T intersex could skew the data to make it seem that intersex high T didn't convey an advantage. I think everyone would agree that in real life, high T does convey an advantage.
In my opinion, a solution might be to handle intersex the way we handle awards at the USATF Masters Championships. Athletes outside the US are allowed to compete and get medals, but they don't bump US athletes out of medals. If the winner is Canadian, for example, he or she gets gold, but the 1st finishing US athlete also gets gold. This happened to me a few years back. I finished 3rd, but I got 2nd because the winner was Canadian.