JSB: 12 x 6.1" is still a reasonably strong armament. The Japanese 6.1 had a pretty good range. That ship would still probably have blown away Argentinas pair.
My last converted light cruiser is based on the KM Nurnberg which was commissioned in 1935. The design has to be reworked to take the twin 8". Lot more breadth, and depth required of the hull. Having more tonnage to play with means the armour can be much more comprehensive.