It's one thing to have a carrier force and quite another to use it effectively. The Swordfish demonstrated that it could be used with devastating effect when combined with surprise. Up to that point, it had never been done on such a scale.
Whether Pearl Harbour was the key turning point or not, I guess Churchill was more qualified than most to make that judgement. Anyway, it's a purely academic point. Thankfully Barbarossa was a tactical blunder which failed through a number of miscalculations, the weather etc. etc. The original question was about a particular aircraft having made the greatest contribution. Which aircraft brought back the captured enigma machine and code books ? Does anyone know ?