Omega Weapon, I think still stands at FFs hardest optional boss behind Penance. But this is only because Omega needs a lot of preparation beforehand. You need to have some Heros, some Holy Wars, a Meltdown (or just Doomtrain) and speed to juggle casting Shell, Protect and Curaga. It's also useful to learn his attack pattern so that you know what's coming next.

You must've done at least SOME of that to have beaten him. So basically you've either gone out and read some article that teaches you how to beat him which isn't really something commendable or you're just lying.