Thicker and longer arm hair is still a masculine trait. Testosterone thickens hair all over your body. Feminising HRT does revert body hair for some people (but not facial hair, it's a biological quirk), but usually not enough to where cis women are if you started out hairy
I feel like harrier arms on women isn't that uncommon, but that could also just be the people I hang around (they tend to be more punk/hippie than the average)
