Why 16-inch Kongos become glass cannons

How would the Kongo class perform if its 14-inch guns were replaced by 16-inch weapons?

They would be powerful but unbalanced glass cannons unless armour and propulsion were upgraded too.

A direct gun substitution makes the Kongo class more threatening to American planners. The hulls would carry much greater striking power while retaining protection designed for the original battery and role. The result is a glass cannon rather than a balanced fast capital ship. Armour and machinery would also need major improvement if the navy wanted the ships to absorb return fire and preserve useful mobility.