You're inverted. 4.65% defense down would only beat 2x Minuet if the monster had some extremely high Defense value (as in, significantly higer than anything that exists in the entire game, so practically never), or if cRatio became capped either way in which case they would be equal. The upgrade from Dia 2 to Dia 3 will never "beat" Minuets on EXP mobs.