A 14-inch North Carolina changes little in combat

How would North Carolina-class battleships with twelve 14-inch guns have performed in the Second World War?

Much the same, because their missions and decisive advantages depended on far more than the caliber change.

The armament swap matters less than the ships' actual service. Twelve 14-inch guns would not change the class's machinery, armor, secondary battery, sensors, crews, or capacity for later refits. Washington's only historical surface action against a major enemy warship would still place Kirishima at a decisive disadvantage. The counterfactual therefore changes the main battery without changing the circumstances that determined the class's wartime performance.