A third category for people with DSDs wouldn’t be big enough. The only reason they are overrepresented at the moment is that some coaches actively went and sought out males who had incorrectly been registered as female at birth when someone spotted what a potential goldmine those athletes represented.
As you say though, any trans category would also have to be split into male and female as otherwise it would merely be an additional category for men. Realistically, athletes who need medication that is banned have always had to make difficult choices. Women, of course, have always had the added complication that the (physically) best childbearing years overlap with the best sporting years. Being a top sportsperson always requires sacrifices, one way or another, unless you are a male in the women’s category, in which case, not so much.