I agree. It can do with some clarification.
Lets make it a “perfect relationship” then. A great loving marriage between a husband and wife. No social issues, a loving relationship. A family raising kids.
Now take that exact same “perfect” relationship and substitute the female from above with a male. Or Vice-versa
Which family structure is best for the upbringing of the child?
It’s a no brainer.
I can only answer that with: I don't know, I've never met anyone in a perfect relationship, and I don't expect to ever. Plenty in good, or even great relationships, but perfect? No.