The main issue with junctioning magic to statistics here, I would think, is that Ultimecia can wipe out an entire stock of a given spell.

That being said, there are plenty of strategies that will allow you to take apart Ultimecia with ease. If I recall correctly, Ultimecia's level is set, rather than leveling up as the party does (like most enemies). Given that, she has an advantage on you, so further leveling will help your cause in this case.

And, yes, The Extreme is an awesome final battle theme.