The Russo-Japanese War and the American Civil War, when naval mines were still called torpedoes, had already shown the weapon's value before 1914. The counterfactual does not claim that more Brummers would have won the war for Germany. The proposed alternative was to build a pair of improved minelayers every few years after Nautilus, a relatively cheap program that would have repeatedly complicated British planning. Brummer demonstrates a practical capability that German planners could have developed from evidence already available to them.
Notable Point · 47:33-49:10
The evidence for mines already existed
The Russo-Japanese War and earlier conflicts had already demonstrated mine warfare, so a pre-1914 German fast-minelayer program did not require hindsight.