Why Northampton-class cruisers did not fit the Royal Navy

Would Northampton-class cruisers have suited the Royal Navy?

Not especially; their US scouting role overlapped British carriers and battlecruisers, while County-class ships better matched British commerce duties.

The US Navy needed the Northamptons as scouts for a fleet organized differently from Britain's. The Royal Navy already assigned much of that work to aircraft carriers and battlecruisers. County-class cruisers were less specialized for scouting but sufficiently capable when required. Their stronger fit was the Royal Navy's wider commerce-protection and commerce-warfare requirement, illustrating why a successful foreign design need not suit another navy's doctrine.