I haven’t even had bottom surgery yet, but thanks to HRT my metabolism is much more in line with that of a typical woman than that of a man. Meaning that it is much more accurate to refer to me as a biological woman than as a biological man. So saying I’m the later isn’t just insulting, it is even scientifically incorrect. A trans woman who has received bottom surgery is in fact for pretty much all intents and purposes the same as a cis woman who has received a radical hysterectomy. Unless you call that kind of cis woman a biological man, doing the same to the trans woman is just as nonsensical.

And yes, this really affects pretty much everything: The treatment of things like brain tumors depends on biological sex and if you treat a trans woman like a man you are going to see the same bad outcomes that treating a cis woman like a man would have. Because again: Trans woman are (from a certain point in their transition onwards) biological women. Yes, it changes, get over it.

The reason to talk about amab/afab is specifically because they are the only terms that are reasonably consistent in all edge cases, except clerical errors.