D I didn't start from R=U at all with those assumptions. I started with the unlikelyhood of someone being named Ultimecia at birth, along with being huge and having facial markings.

Ultimecia HAD to come from somewhere, she HAD to have had a lot of abilities that aren't shown in the game, and she HAD to have gone through all of these changes and aquired a castle and Griever through some means which probably took a long time. How any of this is done is not explained in the game, R=U is just a way to connect the present and future in a way that explains a lot of coincidences along the way.