One can say what they want about Hitler mismanaging the war, but he endorse the radical plan that bumped off France in 6 weeks. That was definitely a world changer.
And that was when he let his generals do their jobs. After France Hitler started to be more meddlesome. I would place the start at the Battle of Britain.
Not really a radical plan, just Schlieffen redux. Schlieffen was the real visionary, but it took Tanks to make his plan work, and he damn near won it all on the Marne in 1914 anyways.