The earlier C class was intended for fleet fighting, and the D class for scouting. The E class addressed surface raiders. HMS Glasgow's experience at the battles of Coronel and the Falkland Islands supplied the operational lesson behind that role. The design was aimed at a dispersed maritime threat, a different problem from the fleet melee assigned to the C class.
Chapter · 5:20-6:08
Why the E class was built for raider hunting
The E class addressed surface raiders, while earlier C and D cruisers were built for fleet fighting and scouting.