Why a single 16-inch gun is poor turret economy

Did designers pursue capital ships with a single 16-inch-gun turret?

Not as a sensible modern arrangement, because a twin turret costs only modestly more and provides essential redundancy.

Beyond the predreadnought era, a single-gun heavy turret offers little benefit on a large warship. A twin mounting is not dramatically larger or more complex, and it avoids losing the turret's entire offensive value when one gun becomes unavailable.