Given a fixed quantity of gas particles, the pressure, volume, and temperature are related to one another. That remains true, just imprecise.
It is not imprecise. It is partial.
The ideal gas law is an accurate representation of one particular physical process in isolation. It is valuable because it is accurate 100% of the time when we exclude or account for the action of other physical processes. That's why this is not a good analogy.
99% of the time, gamete production/chromosomes/genetalia/secondary sex characteristics all correlate, and because of rare exceptions, you want to throw out the rule entirely
Firstly, yes.
If I drop an object 99 times and it falls to earth, but when I drop it the hundredth time it doesn't fall and stays hovering in the air, that hundredth time has far more profound implications for the theory of gravity than any of the preceding 99. That is basic empiricism. Finding the rare exceptions to general principles is a huge part of what scientists try to do, because they are the points that advance knowledge the most.
Secondly, this is not a rule. This is not even the most rudimentary basis for constructing a rule. A rule is a principle which is simple yet accurate and which can be used to construct more complex models. This is a complex model being deliberately oversimplified to fulfil ideological objectives.
There are a vast, vast range of factors which go into determining the appearance of someone's genitals, or their secondary sex characteristics. All human beings have some degree of variation in the appearance of their genitals and secondary sex characteristics, regardless of assigned sex, because all human beings are subject to countless genetic and environmental variations which impact these things. The appearance of your genitals is not scientifically significant, it's merely the end result of a complex and far more interesting process. It is socially significant, but only because it has been socially significant long before anyone understood anything of the mechanisms by which it was produced.
Biology cannot magically create a coherent social meaning of sex, and it certainly cannot assign that meaning any kind of metaphysical or teleological importance. That social meaning of sex existed before biology existed, and biology will exist long after that meaning is gone. Appealing to biology is merely trying to add a façade of rationality to deeply unscientific beliefs about the meaning and purpose of human life.
You are not trying to grow or develop the understanding to capture the exceptions to the simple rule, you are denying that there's anything physical there to understand in the first place.
There is a huge ammount to physically understand, once you understand that none of it will give scientific credibility to the meaning our society has historically assigned to being a "man" or a "woman".
You missed out some of the most important and interesting bits in the whole process. What about gonadal cell determination and later composition? What about the SRY gene? What about the hormones that actually do the work of creating the physical structures of the genitals and secondary sex characteristics? There is a complex and fascinating machinery at work here. None of it, however, will ever explain the existence of men and women as social categories. None of it will produce the natural, sex complementary social order you want.