>>I believe that the only true determination can be ultimately done by the person themselves. >>

In the cases of some of the more complex DSDs, you need to be a medical specialist to make a determination of the person's sex. This doesn't make any difference to how they want to determine their gender. But in some cases, streak gonads can become cancerous (and sometimes male streak gonads are more likely to become cancerous than female ones), so it is important to make a determination.

I think you are confusing sex and gender. You describe yourself as "likely considered to be in that 0.2%" but I don't know if by that you mean you have been diagnosed with a DSD (in which case yes), or just that you identify as trans (in which case probably no).