Damage calculation formula is here: Damage Calculation
So +100% attack equals -50% defense, so full BK buff (+145% attack) is slightly more than -54% elemental defense from Falcon. But Falcon do some damage too, while BK doesn’t. And you don’t have to wait one round till you are hit (to get to +145 % attack).
Note: The damage calculation formula doesn’t work when you get over certain attack/deff ratio (around 8 I believe). So if you tried to calculate titan damage for example you would get much higher numbers than you would do in realitiy in-game.