I think you are forgetting the Aedra. They most certainly are not Deadra after all.
The game has many powerful NPC's I am going to need to go with Almalexia in addition to her personal powers she has a literal army of followers willing to meet her every whim.
I wish, however, it were Ayrenn.
** Asus Crosshair VI Hero, Ryzen 1800x, 64GB DDR4 @ 3000, GTX 1080 ti, 4K Samsung 3d Display m.2 Sata 3 Boot Drive, m.2 x4 nvme Game Drive **
If goddesses are off the list, I'd say Alessia back in her time. Badass queen, favoured by gods, who ended human enslavement at the hands of the Ayleids and became the first Empress of Cyrodiil? Can't get much better than that.
Present-day, I'd agree with probably the Lava Queen.