Not at all. You juets need to use KOTR with one character and then Mimic it as many times as you can manage. If you have the Underwater Materia the time limit goes away as well. Most people consider Emerald Weapon much easier than Ruby.

I would say Ozma was the worst of the bunch. He gets like 3 attacks before even one of your characters can take action. By that point, you've got maybe one character still standing and he's fighting to stay alive.

By the way, I really think Omega Weapon from FF8 should have been included in this. I just barely managed to beat his ass because Phoenix was so kind as to auto-revive my entire party once during the fight. If it hadn't been for that, I would have been roasted.