Whether something classifies as a primary or secondary characteristic is mostly only of interest to biologists and people involved in medicine. The classification refers purely to biological matters and development during puberty.
If someone were to make a Rule 63 of the Rule 63 would look like Power Girl, because massive genitalia is not what society considers “sexy” in women – but massive boobs are.
What’s really interesting to me is the disregard for all the other aspects involved. For example, Power Boy’s lips remain full and kissable but his upper body is more bulked than Power Girl – but not as ripped and chiseled as conventional super heroes are.