The modern case for a twin-gun mount

Which concept should have been developed further for modern use?

The twin-gun mount, because two guns could give a warship a faster and larger volume of fire against threats where shot volume matters.

Single-gun mounts have defensible advantages, but some reasons for abandoning paired guns are presented as engineering problems that could have been solved. Two barrels in one mount would deliver a greater volume of fire in less time. That rate matters against modern threats that may demand multiple shots. The case for continued development rests on the volume of fire available from one mounting.