Depth competes on a different level. Depth works when a market becomes cheap enough to cater to (or the market is so large that a small fraction is worth it) that you get long tail economics. The benefit for the producer is less cost petition. We're almost there with television. We're almost or possible already there for some select markets for YouTube, but coming from the other direction (high production vs low production).

More accurate to say breadth tends to scale bigger, and depth allows for focus and better product/market fit in a smaller market.