I seriously think you're onto a loser at this point, but also worth pointing out if he wants to play with linguistic racist hoops:
Ok, fine. So by his logic black women are women, white women are women, disabled women are women transwomen are women yada yada yada. The adjective just describes the woman. (If you squint a lot, twist sideways and overlook that trans actually means born male).
So he's ok with disabled women having groups and spaces etc that only disabled women attend, right? No able bodied people speaking for them/over them/arrogantly insisting they know better what disabled people need and want and feel?
And ok with BAME groups for BAME women, and the right to demand only BAME voices or people for certain things? No non BAME people dictating their experience? (He should be nicely fired up on social justice warrior mode by now, hell yeah etc etc)
LGBT+ women? All the same? Same spaces, right to choose only LGBT+ professionals/counsellors/groups/not to have policy imposed by non LGBT+ women?
Ok. Female women get the same rights then.
All the above. All the same reasons.
Watch the gears grind.