It's not a one or the other situation in ration to chromosomes or hormones.
I do think this is a real casualty in the ideological drive to just change the category of 'women' to include transwomen, but without looking at the different ways we use that category, why having different spaces/events for women is justified, and exactly what boundaries make that category work as intended.
I think it would be more helpful to be a bit more thorough in considering each of the various situations where we treat men and women differently, and for each situation agree the most inclusive way that still fulfils the intended purpose - ie why it's OK to treat men and women differently in this situation in the first place!
It really isn't transphobic to recognise that there are genuine differences - between men, women, transwomen, transmen, medically transitioned/not - which sometimes need to be taken into account to be fair to all.