So no, we might not ‘equally’ argue that those who support trans rights are trying to ‘erase the female sex from everything’.
I had in mind the way in which the female body is now being turned into a gender-neutral one so that those of us who have embodied identities are now told that we are gestating parents, not mothers, or vulva people, not women, or uterus-havers or menstruating people and so on, while nobody much is interested in turning the male body into something gender-neutral by writing about impregnating parents rather than about fathers, or about penis people, not men, or about prostate-havers or ejaculating people etc.
And yet demands for inclusion should cause exactly those changes in how 'man' is defined. They do not, and that's why it sometimes looks very much like the eradication of the female sex as something that can be mentioned might be an intended goal here.
These linguistic and social changes which are now demanded almost entirely go in one direction, which is towards the erasure of female people.
I see Dylan Mulvaney's adverts for female clothing as part of this overall trend. I would be perfectly fine if Mulvaney said that these clothes are great for trans women, for instance, but that is not the message of that Nike ad.
Rather, the message seems to be that Mulvaney (who is not a girl, even agewise) should now be regarded as a girl in that ad, even if it's a parody of a pre-teen girl's possible behaviour.