Regardless, if you were able to hit a large artillery shell coming at you at the speed of many rifle projectiles and hit it; would you feel fine just standing there as the remaining pieces came at you at close to the original velocity?
People have a Popular Mechanix view of the effectiveness of modern defensive systems. They will never be anywhere near 80% or less effective.
Throw in the inevitable fog of war, the sailors that cannot steer out of the way of a huge cargo ship..........
CIWS does well against sequential threats - but it is still vulnerable against saturation attacks and jamming. Sea-skimming missiles, big or small are also a complex problem for the CIWS.
Oh, and we took the CIWS off most of our naval vessels and replaced them with Sidewinder missiles in box launchers. CIWS can’t defend a ship if it’s not there.
If you are down to CWIS the shit is wide and deep. Only a few seconds worth of run time and minimum of five minutes to reload. Five minutes is an eternity if missiles are inbound.