20 may seem to be a small number of laser turrets, but these turrets are auto-lock and multifunctional; Instead of only destroying planes and missiles incoming to the Nightingale, the turrets can also engage to any ground/naval unit the system thinks can be destroyed easily/is in close range. The lasers of the X350 is also much more intense. If a split-second shot from the ASCAS's laser beam can create a perfect 50 centimeter in radius hole in your body, the X350's can completely disintegrate you and people and structures surrounding you at the range of 20 meters.