"Assigned male at birth" and "assigned female at birth" are not meant to be stand ins for "biological sex." They're meant to be what you were *assigned* by other humans. There's no such thing as an "amab body" or an "afab body."

These were terms meant to highlight how gender is imposed on us not divide people into who produces the large gametes or small gametes and if you take "trans women are definitionally AMAB women" to mean "You're saying only women with penises can be trans women" then you're either

deeply mistaken or interpreting in bad faith. Either way AMAB and AFAB aren't meant to say "You have a specific set of reproductive organs." They're meant to say "You were put into this box and that box and expected to live accordingly."

These boxes cut across intersex and trans bodies, often violently. If you're intersex and assigned male it doesn't matter if you were born with a vagina or not, you're still AMAB'd and no one's saying you aren't or can't be.

These terms are supposed to refer to history *not* gender. They're not meant to say what someone's sex or gender is.