It's worth taking a step back to consider why we have separate categories for male and female sporting competitions, which is: the significant physical advantage that male development confers on an individual. If sports were mixed-sex, males would dominate almost every competition. So we have women's and girls' sports separate from males, to recognize and celebrate female athletic excellence.
With that in mind, it should be obvious why exclusion of male athletes from the female category is necessary: for fairness, and in contact sports like boxing, also safety.
The reason that males with 5-ARD have testosterone levels in the normal male range is that they have testes which produce it. They go through male puberty and thus have bodies which, in a competitive sports context, have the physical advantages conferred by male development.
These males have no female organs. Some develop a perineal pouch which may be mistaken for a vagina, but it isn't a vagina in the female sense - not anatomically nor histologically - and certainly isn't functional, given that the function of an actual female vagina is copulation and childbirth.
Whether they're raised as if they're female or believe themselves to be women isn't relevant in the context of competitive sport. The reason they should be excluded from the female category is the same as any other male: the categorical advantage from male development.
This is why it's so controversial that every medal winner in the women's 800m at the 2016 Olympics was male, and that two males took gold in women's boxing in the 2024 Olympics.