I haven't done much investigation of the PC side, but all boss physical attacks in the stat topic do Atk x Power - Def damage. Power is usually 2, but sometimes 1.5, 2.5, or 3. The only exceptions are Harken's weird moves, but they certainly don't seem to factor in Def any more than normal (if at all). So yeah, on paper, 25% of the raw Def stat should be absolutely pathetic. If it's more effective against any DL bosses then the move must have some other effect (again, I didn't use the buffs enough to say).