The starkest example to me of breadth first vs depth first learning are math geniuses. They typically ignore everything except mathematics to begin with and then hyper focus on a specific area of mathematics intensely. The most striking I know of is Peter Schulze who basically never attended an undergraduate class in mathematics and picked up Linear Algebra while he worked out the requirements to understand the Langlands Conjecture. He got awarded his bachelor by doing a 6 hour exam when he entered University.