I wasn't thinking you were denying bodies are what they are (though you might do so if I was to talk about some intersex bodies).
My point the idea of sex you are using claims bodies
are more than bodies. If I take a body, let's say one with XX chromosomes, a womb, breasts, a vagina, etc., your position proclaims it
must belong to the sex category/sex identity of "female." It is subsuming our linguistical/conceptual/social practice of "female sex" into the body itself. You say such a body must be "female" when such a categorisation is not actually given in the existence of body.
A body with XX chromosomes, a womb, breasts, a vagina, etc. might be categorised any number of ways. We might have such a body and not refer to it be a sex at all. We might categorise such a body as "male ". The body itself doesn't pose a meaning of sex itself. It will be a Y chromosomes, a womb, breasts, a vagina, etc., not matter which category we place it in.
A body being present doesn't suppose anything "male" or "female."
This is why people using your categories have to say:
Well, that body is
definitely female because XZY...". If the present of a body did suppose sex, we wouldn't have to suppose an extra understanding over the body we already know. I would be able to think: "There's a body with XX chromosomes, a womb, breasts, a vagina, etc." and understand them "female" without engaging with sex as a distinction.
Yet, sex is a distinction. It means something distinct to "there is a body with...". Sex is not contained within the body. It always remains a seperate concept/meaning. The step of placing the body in the extra meaning of "sex" has to be taken.