Siegfried with 2x Belial, -50% DEF down, maxed Assault, +30% character ATK from Svarog, Union ATK and Burst buffs, and elemental advantage might be able to hit 1 million damage. But... what's the point in setting up the perfect scenario just to see your damage nerfed? I'm not sure what this proves. It's certainly not a necessary or sufficient condition to clear content or understand mechanics.