How would a larger County-class cruiser be armed?

If the County class displaced roughly 15,000 to 18,000 tons, would its original 1920s armament still be enough?

The main arrangement might remain, but extra tonnage would likely add four-inch guns, pom-poms, and possibly more torpedo tubes.

The counterfactual keeps the design in the technology and threat environment of the 1920s. Likely changes are evolutionary: paired or additional four-inch guns, more quadruple pom-pom mounts, and possibly a larger torpedo battery. Extra tonnage would not automatically produce a radically different main battery because doctrine and available weapons still constrain the design. Displacement buys choices, but designers spend it according to contemporary priorities rather than later wartime lessons.