I may be wrong here, but I always thought the corkscrew was meant to get the aircraft out of searchlight cones. This would also have had validity in escaping from the early AI systems which had limited range and azimuth capabilities. Not so sure your spitfire pilot was operating as a night fighter pilot over Europe to offer a truly informed comment. For the big 3 bombers, (Lancaster, Halifax, Stirling) there was a criminal lack of ventral defence, IIRC very few ever had a credible installation to discourage the Nachtjagdgeschwader from attacking from below the aircraft. One suspects that the development of schragemusik installations and the increasingly skillful use of GCI and AI was indeed the cause for the high rate of loss amongst the bomber streams.
Just a thought, respects to all who fell