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I have to admit that I'm not massively knowledgeable on pre war bikes metallurgy, and was just making a sweeping Internet assertion. If I had to bet, I'd say that the amount of material they'd have used, as well as the glue, would have brought it to a pretty similar weight. Let's find a pair, I've got a fiver on steel. Everyone should really use steel bikes I think. And buy from local firms.... ;)
Weight advantage is relative anyway. Cut two comparable bikes apart today, one aluminium and one steel and see the wall thickness disparity.