I haven't played the PSP version yet, but Balthier would have to have some wicked skills to beat out Ol' Thunder God.

Orlandu can do tremendous raw damage per strike, but he's not always the most useful character. Beowulf has a lot of Temple Knight skills that come in handy when you want to incapacitate foes instead of killing them (like for teaching Zodiac or finding the exits to Deep Dungeon).

Naturally with stat manipulation you can make other characters more powerful than him, but he comes naturally with high stats that complement his Holy Swordsman attacks.