Why Type 31 has an unusually light mixed gun battery

What is the oddest gun loadout on a modern warship?

Type 31's one 57 mm and two 40 mm guns: logical as a flak battery, but unusually light for a general-purpose presence frigate.

Type 31 has the oddest modern gun loadout offered in the discussion. Its 57 mm gun and two 40 mm mounts create a coherent rapid-fire flak battery. The unusual feature is the absence of a heavier weapon on a frigate intended for general-purpose presence and task-group work. The defensive logic makes sense, but the ship's mission calls for more weight and reach. An earlier proposed redesign replaces the mixed centerline battery with multiple 76 mm guns.