If I have a champ whose damage scales off of defense, and I give them a 50% increase ATK buff, then will that champion do 50% more damage? Or will the buff be useless?

Same with increase DEF buff. If a champ's damage scales off DEF, and I give that champ a 60% Increase DEF buff, will that champ do 60% more damage? Or will they just take less damage from incoming hits?