As in most other Final Fantasies, it's quite possible to win the game without the ultimate weapon, and it may even be more convenient seeing as there's no tangible reward for getting everything, except a short little cutscene in X-2 that I downloaded off of LimeWire to save myself the trouble of actually playing the rest of the game (it almost made me retch after a mere ten minutes of play).

I got enough of the crests and sigils to get most of my aeons to break the damage limit; beyond that, I didn't care too much. One of my friends screwed around for 164 hours getting everything. Every character did 99999 damage per hit.