OH he's not difficult, its just the things you have to do in hte lead up to him that make it hella difficult.
Essentually the situation, as i read in a strat on Gamefaqs, is that the final boss is unbeatable untill you beat the 4 other final bosses. This is becuase the final boss has an instant kill whole party attack which it ususally uses in the 2nd or 3rd round of combat. Defeating these 4 other bosses reduces the final bosses starting health to about 20k or so which you then have a chance to kill it before it wipes your party out.
So first you need to defeat these 4 other bosses which are apparently really hard in comparison to the final boss and the only reason the final boss is considered harder at all is cuase of his kill all ur guys attack. Now i say apparently cause i was never able to even locate these 4 bosses! Thats right, its not a matter of they were too hard for me or anything like that but that even with the help of a walk through i could not locate these 4 bosses and therefor could not have any chance vs the final boss.
But while writing this i went back to a walk through to re read it and appparently you are supposed to get killed by this final boss then get revived and go into some sort of shadow world or something. Now i'm not someone who just shuts the game off if i loose a boss fight but it is possible. I guess i miss read some where and thought that you need to find these other bosses BEFORE encountering the final boss which lead to a couple hours of frustrated searching with no results.
But anyways hte game itself was lacking imo, way too quick and not a whole lot to do outside of random encounters where you just use the same move everytime depending on you Jobs.