TIME PARADOX!

[Wolf Kanno]

There are three ways to look at this:

1) Despite being trapped in a time loop, Ultimecia will eventually succeed cause her powers grow each time the loop is replayed meaning she will eventually beat Squall and Co.

2) She can never succeed cause VIII all but states it exists within a deterministic world meaning no matter how strong she gets, she is always fated to be destroyed by Squall and Co. cause everything in the VIII world has already been predetermined.

3) You're not suppose to think about this cause the writers didn't and you should just stick to the idea that Ultimecia is a badass time witch.

If you want to get into baseless speculation, I would say that its possible that all Sorceress' powers are suppose to be equal but in reality each one specializes in one aspect over all others. For instance, Edea has an Ice elemental theme which can be seen from her Limit Break and weapon whereas Ultimecia shows the ability to make inanimate and intangible objects become real such as the statues in the Parade scene or Griever. If you look at it this way, then Ultimecia is simply trying to gain and merge all the different proficiencies together to make her like Hyne. So the ability to use magic without the use of a GF or Chi is a base ability all sorceress' possess but it is not an ability that is any stronger than others; rather its the specialized ability that Ultimecia is after. I of course have no real proof and god knows the VIII Ultimania and the game itself offers no evidence nor does it actually bother to explain anything at all.