Changes in legal or morphological sex is not relevant. This is not what we are discussing.

Of course they're relevant. Sex being immutable, easy to define and binary is at the core of the tactics that transphobes use to exclude and legislate against trans folk.

So the fact that it's not easy to define, has multiple definitions in different contexts, and has no single definition that works in all instances is very relevant.

You talked about "genetic bio-chemical reproduction" earlier. There are women who have literally given birth, who have XY chromosomes. Similarly, there are XX men with SRY genes. Using your "genetic sex is the truth" approach, they are both folks with a different genetic sex to their physical and legal sex. A transphobe would catch those people and throw them under the bus too whilst they target trans people.

The bio-chemistry of terrestrial life is built upon a binary sex framework

Yep. I'll agree with that. But the framework it is built on is not the end result. There is no meaning or intent behind the framework. There is nothing about it that is more "real".

The real part isn't the genetic plan that was used to create someone. The real part is the body they're actually walking around in.

To you, this is all an interesting argument. You're arguing about things in black and white, because none of it actually matters to you. So you can argue for how you think things should work.

The very same arguments you are using are being weaponised and turned against gender diverse folk and intersex folk. Your re-use of them, arguing about some sort of ideal that exists only in your head isn't harmless. The fact that sex is nuanced, that gender is nuanced, that they both have multiple, contradicting definitions, and neither have a single definition that is more true than the others is incredibly important, because the only reason to ignore that is either to hurt people, or because you're so far removed from the reality of what's happening, that you place a higher priority on things being neat and tidy than on the people that false belief hurts.