"What if woman biiig" is the laziest and therefore best form of worldbuilding to create a matriarchy.

But, how biig, and how to biig?

The first and most important impact of women biiig would be on population collapse and demographics in premodern societies. An unbelievable number of women historically died during childbirth, and a mother of two who dies on child three often ultimately meant four deaths by household collapse. That number would be much, much lower if women's hip sizes had been intelligently designed by a woman-loving deity, or if bone evolution had not been slower than social advancement. Human childbirth is unusually dangerous among mammals and even among primates because of the skull to hip problem. However, babies, including woman babies, do continue to grow outside of the womb and this does include their brains, it is entirely possible to have woman biig without making babygirls so biiig that the effect cancels. That affects not just the way pregnancies are managed but also things like raw demographics and social demographic necessities. The trouble with trying to worldbuild after changing something so crucial to social customs and division of labor is that this seems like a really, really radical change. Ease of childbirth under a woman biig scenario makes stable female populations more or less universal, and a lot of the oldest stories in the world seem to involve some element of bride abduction which suggests that that just wasn't ever the case in human prehistory. The transition to agriculture wasn't a precondition for civilization for reasons of permanency or nutrition, it was because it aided social organization modes that helped keep birthgiving populations stable and this is not just a division of labor thing since all known nomadic cultures also had divisions of labor.

It is often proposed that matriarchy should start in the womb, or in the school, or the strength of the arm. I propose that it would instead start at the hips.