The evidence strongly suggests that’s correct. Once set in the womb by neural development in the third trimester, the resultant development paths are tightly constrained, regardless of post natal hormonal environment. Of course, as physiological characteristics such as genitalia are formed earlier, gender and sex may be discordant.
“There are over 6,000 genetic differences, affecting everything from the skin to the brain.”
But a bone marrow transplant changes that. Or can do.
See Bone marrow-derived cells from male donors can compose endometrial glands in female transplant recipients by Ikoma et al in Am J Obstet Gynecol. 2009 Dec;201(6):608.e1-8 & Transplanted human bone marrow cells generate new brain cells by Crain BJ, Tran SD, Mezey E. in J Neurol Sci. 2005 Jun 15;233(1-2):121-3 :
It’s really only important when measuring statistical sensitivity to various chemicals. 46,XY mothers exist. 46,XX fathers exist (though far fewer than 46,XY mothers, apparently). And of course 47,XXY people exist.
“The very “best” options are still merely cosmetic.”
A matter of opinion. Womb transplants have proven to be very successful for some Intersex women. It’s only a matter of time before they’re made available to Trans women with similar physiology. And in order to justify that “cosmetic” opinion, you’d have to justify why you’re picking one set of physiological characteristics – say height – over another, say bust size. Or vice versa.
I think you’re right in your opinion, but I have no idea how I’d go about justifying that, and could easily be persuaded to change my mind.
It’s anything but simple. Sorry.