Why the Leanders felt like stepping-stone cruisers

Why are the Arethusa and Town classes preferred to the Leanders?

The Leanders restarted light-cruiser design after a ten-year gap and became stepping stones whose compromises were refined in later classes.

The Leanders are rated below the Arethusas and Towns because they were stepping-stone ships whose design accumulated compromises before later cruiser classes refined the idea. They were the Royal Navy's first new light cruisers after a gap of roughly ten years since the E class. Designers had little recent experience to build on. The class had to re-establish a development path that its successors could improve.