Spiteful and Seafang extend a proven design line

What was the purpose of the Supermarine Spiteful and naval Seafang programs?

They attempted to keep a proven and comparatively cheap design family useful by evolving it into a higher-performance successor.

The programs tried to extract further performance from an airframe lineage British industry already understood. Continuing an established family could reduce design risk and retain familiar production methods. The naval Seafang extended that logic into a carrier fighter rather than discarding the accumulated experience behind the Spitfire line. Comparative viability and cost matter as much as the aerodynamic ambition of the new aircraft.