I beat Omega in 3 minutes...I was VERY disappointed in him. Was my fault though, I forgot all about him and suddenly remembered after all my characters were Sphere-Grid Death Machines
The monsters at the arena are a bigger challenge & if you have the balls & PAL Versions, the Dark Aeons are a fantastic challenge.
But yea, I just hacked away at him, no real tactics, just a lot of hacking & he went rapidly.