No he is not that hard, read this if you're going up against him:

Battle Preperation

You'll want to have as much auto regenerative ability stones equipped to your characters as possible. Auto-Life, Auto-Potion and Auto-Regen are must haves. HP increasing stones, such as HP+20% are also helpful. The strongest weapons and armor you have will need to be equipped. Equipping the add-on Pumice Piece to your party members is extremely important to protect against Shadow.

Ozma will attempt to silence your magic casters, so make sure they all have the Loudmouth stone equipped. He'll also try to inflict status damages as well, so equipping stones such as Antibody and Clear Headed are recommended.

It's also recommended you work your ideal attack party for this fight up close to their Trance modes, to take advantage of their skills.

Battle Engagement

Luck is a major factor in winning this battle. Although your characters may strike for powerful damage against what seems to be a small number of total hit points, Ozma will unleash a horde of attacks to eliminate you. The key is to keep on top of his attacks immediately after he inflicts them upon you. If any party member has at least half their HP, you can be sure they'll be the first the go down. Double magic attacks are extremely helpful and keeping your party fully healed at all times is necessary. Make sure you heal constantly with magic, skills, Eidolions, and items. This is the toughest battle in the game, so when it comes to using your items and skills, you definately want to splurge. If you have any Dark Matter in stock, use it as much as possible. It will deal a full 9999 damage.