Witness an assortment of asks sent to a blog that posts anons identifying as AFAB transfems:
You say “these labels aren’t talking about genitals” but clearly a lot of the people identifying with them are talking about genitals, and, more broadly, about having “male” bodies or bodies with features that are considered “male”.
The usual definitions of transfem and transmasc don’t refer to any physical feature: a transfem, in the definition of someone who was assigned male at birth and then transitioned to a more fem identity and/or presentation, could have any genitalia, any hormone balance, and any physical appearance. They could be pre-, post-, or no-HRT, bottom surgery, top surgery, hair removal, and/or FFS. She could be intersex, with any chromosomes, internal anatomy, and endogenous hormone production. There is nothing exclusionary of intersex people about describing social experiences as related to gender assignment, a phenomenon which notably shapes intersex people’s lives.
You say “they’re talking about the intersection of being trans and identifying/presenting in a masc/fem way” as though using “transfem” and “transmasc” to mean “fem” and “masc” is somehow more inclusive and less binarist than using them to mean “assigned… transitioning”. The terms fem and masc already exist, are already used to refer to people’s identities and presentations, and already net plenty of complaints about being binary in concept and use.
The usual definitions of transfem and transmasc encompass people with nonoverlapping identities and presentations! Someone who was assigned male who identifies as a butch woman and presents exactly the way she did before she transitioned now with added pronoun pin can ID as transfem and someone who was assigned male who identifies as an agender femme who dresses like Margot Robbie Barbie can ID as transfem and someone who was assigned male and identifies as a bigender drag queen/king/nonbinary monster and dresses every way they’re physically capable of putting together an outfit can ID as transfem.
You say “it just presents another form of binary thinking if there is no flexibility to these labels” but there is flexibility in these labels! There is ample flexibility and the communities around them are incredibly diverse in identity, presentation, body, and life history. They are not exclusionary of nonbinary people, multigender people, or intersex people, they just each only apply to the nonbinary, multigender, and intersex people who they apply to. You do not do a service to these people by telling them that the functional, consensus definitions of transfem and transmasc exclude them and deprive them of language and hurt them or that the solution is to repurpose those words to mean fem and masc.