Well it highly depends how you look at it Ultimetia can compress time basically ending all existance
Sephiroth can summon a huge Meteor to destroy the Solar System
Kuja sucessfully destroys a planet
Necron can end all existance
Kefka has the power of the planet
The Emperor dies and becomes the King of Hell
Sin terrorizes Spira for 1,000 years without being stopped
What do they all have in common? They all end up being defeated by the main heroes. No matter how they say they are immortal they are defeated. So the entire thing is basically a tie. Besides destroy the world or destroy all existance it all comes down to the same thing the end of mankind and that is all mankind truly cares about