I can sorta agree with Vivi22 here as I have all but Yiazmat and Omega Mk.XII to deal with in this game and my party is in their mid 70's last I checked, I'm usually surprised to hear how often people max out their parties levels but I've yet to see a real point. A proper Gambit set-up can allow you to tackle much stronger creatures quickly than just power leveling. My only reason for not beating Yiazmat (he's like down to a few life bars if I remember correctly) is cause I simply got bored fighting him. I took down Ultima, Great Behemoth, and the Shadow Seer when my party was in their 50's which is about the level needed to beat the game.

You just need a good set-up of equips, Gambits, and just stay on your toes and you can beat down the Final Boss, the most aggravating ability he has is the Palings which allow him to get several free hits on your party.

Otherwise, I'm happy he was a bit more challenging than previous FF Final bosses.