This thread was specifically created to end that myth. They do not share the same base model for each body type (and the whole concept of body type is arbitrary in the first place, it just so happens that certain models have comparable sizes but they're not the same). Height and proportions have more to do with a design language (i.e. how does MiHoYo want the characters to look?) than with a common mesh (for which no evidence exists).

I also compared the heels of the tall females, and while it's clear they were designed in a similar way, they were unique enough that they may as well have been created from scratch.

Similar animations has little to do with the model meshes, I didn't touch upon this. Same concept for poses (which are animations as well). The same base animation is certainly used for various character types with minor adjustments to match their individual joint positions. So while the movement logic is shared, the net result is technically different.