Of course, you need auditive input to study music (although interestingly medieval education would have disagreed with this). But visual depictions also help a

Of course, you need auditive input to study music (although interestingly medieval education would have disagreed with this). But visual depictions also help a lot with music theory. Seeing the structure of, say, a sonata's first movement visually makes it easier to understand certain aspects of it. The same is true of understanding relationships between different keys (e.g. the circle of fifths). It's not an either/or, you need both.