> It most certainly has not.
It has, but, again, mass market clothing doesn’t use it. Bespoke clothing and tailoring does.
> Even in men's legwear where your clothing is more or less fully defined by two measurements (waist circumference and inseam length),
No, those are what mass-market panta tend to use as nominal size dimensions, with variations in the relation of those and other standard dimensions being brand or style variations (where there are options for some of them within a brand, typically multiple of them are collapsed together under another single axis like slim fit/classic fit/loose fit, which tends to lump ankle)
The standard measurements for men’s pants include all of:
waist circumference
front and back crotch length
hip circumference
waist to knee length
knee circumference
thigh circumference
calf circumference
ankle circumference
waist to ankle length
inseam
(sometimes, some of these will be estimated based on visual inspection and the other measurements.)
> there are lots of variations between brands for garments with the same nominal size.
Yes, mass market clothing nominal sizes have no consistent relationship to even the things the subset of measures they noninally represent.
> Let's not even get into women's clothing where you can have such ill-defined terms like "size zero".
The only difference between women’s dress sizes and men’s pants sizes is that the former is a one-dimensional arbitrary ordinal category and the latter is two dimensional, and pretends to a (false) correspondence to a standard length measurement.