"But making movies and books and other forms of unnecessary art still makes hundreds of billions of dollars of revenues every year."
Everything else being equal, I would not choose these markets. Why? Because these markets are too sexy and too crowded: too much people write games and books out of enthusiasm. (I was one of them.) If you are a game enthusiast, sure create an indie gaming company. But if you somehow can get excited about a business problem which is a pain point for some people, then it is better to choose that imho.
I would say:
Make something people need, and avoid overcrowded markets where a viable business model became problematic (e.g. free is the default) because of oversupply (like tools for professional developers)
I would say:
Make something people need, and avoid overcrowded markets where a viable business model became problematic (e.g. free is the default) because of oversupply (like tools for professional developers)