Sure, it would be startling if that weren't a big part of it.

It also probably relates to whether fetuses gestate inside you or not, and to whether you lactate. It might relate to how you bond emotionally to a one-week-old, though then again it might not. It might relate to the selection criteria you use to choose mates. It might relate to the selection criteria you use to choose allies. Etc.

If we actually want to understand "what gender is," it behooves us to understand the things that it relates to and the things that it doesn't. And because each of those things is being altered by social changes in different ways, knowing what gender actually relates to helps us predict and understand the effects of various social changes on people of various genders.