And one thing that pisses me off on FFX is that Anima, doesn't take off more than 99,999 when he hits the enemy like 25 times, and literally tears them apart. Also the Magus Sister's Combined overdrive is way too overrated. IT SUCKS COCK!
I think Omega is referring mainly to the amount of damage caused by an attack in battle, and Kuja's Ultima attack dropped all of your characters down to 1HP, if I remember correctly. There are certainly more powerful attacks than that. Few that are cooler, but certainly a lot that are stronger.
What about kuja's Ultima attack...he whiped out a whole planet with that.
Now if you want to talk about destruction, Sephiroth's apocalypse, or Ultimecia/Griever's move Great Attractor, eliminates four massive planetoids, and Earth. Also I though a really sweet move was the enemy skill, Pandora's box from FF7. You get it from the Zombie Dragon in Sephiroth's Crater.