Funny enough, vanity sizing strikes there too. The purported waist size of a pair of Levi's is off by almost three inches.

One might argue that the size on their label is not supposed to indicate the size of the garment waistband, but the waist size of the wearer who would find it comfortable, but even with that interpretation it doesn't work out right.

Yeah. It's a remarkable problem. There is a clear solution that is happily used for men. You tell people what to measure then have the clothes sized for the various dimensions.

Charles Tyrwhitt have this guide where they tell you what to measure for shirts :

https://www.charlestyrwhitt.com/au/size-guides/szg-formal-sh...

and for trousers :

https://www.charlestyrwhitt.com/au/szg-trousers-4-2021.html

Presumably some online shops for women have something similar?