Most of the details are in the paradigm shifting piece of work Damage Calculation by the revered @SolemnWolf
I believe that the % is based on the attack stat, so 462% of 789.
(This is most easily seen on a titan who does 100% damage to all enemies - all your heroes are hit by one normal attack.)
But attack and defence have a non-linear relationship, so that does not translate into a damage result exactly 462% greater than normal.
I’m sure someone like @Gryphonknight or Kerridoc will correct or expand on my answer if necessary.