Yeah, Chaos is non-elemental, so for once you don't have to worry about healing enemies. Going back to the weapon, may I suggest focusing on other side-quests, but using Vincent + Slash-All as your main offense in random battles? That way you don't go insane trying to power the weapon up, and you get other side-quests accomplished, too. Maybe focus on leveling up materia but of course using Vincent. Just a mind trick I learned a long time ago.