You're making a basic mistake between gender and sex. Gender is a social category, and women as a social group are oppressed in various ways. A major task of feminism is to identify and end gender-based oppression. None of that depends on a biologically-determined notion of womanhood.

You're also making an extremely lazy mistake about "average distance between physical traits". I would absolutely trust the capabilities of an all-female fire dept. Not least because people who get into firefighting are not average physical specimens, they have to meet some standard of physical fitness. If a man, woman or gender nonbinary person meet the requirements (btw i think we're both buying into an exaggerated notion of the physical fitness of firefighters), then what reason would I have for doubting their capabilities? Would you want to be saved from a burning building by a team of men with the build of a computer programmer? Gender is not the important question here, and that should be obvious.