Hello GG
I feel the English expression "superior to me" comes from a Latin phrase "me superiorem (elder than me)" where "me" is the ablative case of the pronoun for the first person singular but incidentally the same in form as the accusative "me". On the other hand "my superior" might have its root in the translation of the Greek expression "mou presbyterion (elder than me)" where "mou" is genitive.
paco, another grammar geek