Would a better dual-purpose 4.7-inch gun have materially reduced Royal Navy destroyer losses to aircraft?
Short answerYes; fewer early destroyer losses would leave more escorts for later operations, improving fleet air defence over time.
NotesA 4.7-inch mount with real dual-purpose elevation would have made a major difference to destroyer survivability. Even if many losses still occurred, saving 15 or 20 destroyers would strengthen later operations because more escorts would be available to provide air defence. Small mount-design choices can compound across a fleet's wartime endurance.