i am going to prove right here and now that ansem is not the superior. in CoM Reverse/Rebirth Zexion says he has identified some one in the castle who smells like the superior. after you go through another world another cut scene comes up.
zexion: i have identified the scent, it is riku.
lexeaus: but how riku and the king were lost when sora closed the door to darkness!
zexion: riku once cradled the darkness, perhaps that made him half dark.
vexen: i see, perhaps that is why you mistook him for the superior.
so you see ansem cant be the superior. the superior uses light and darkness. ansem is all dark, he doesnt use the light at all.