Very impportant remember that five hammer only improves your max damage, so if your min damage triggers and wont transpass the mdef wall, your DPS will be a crap.
Fireball have a base damage very low and your final damage comes from agny buff, however in formula, only the base damage will be applyed against mdef.
There was a time after the level 300, I felt like a useless in terms of DPS because of MDEF wall + Five Hammer and your randomic damage.