Indesign is the main graphic software after Photoshop. Basically anything that gets printed uses Indesign. Photoshop is more well known because people love photography as a hobby but in professional print setting photos are just smaller component.
Affinity has an InDesign competitor, so this would seem to be a point in favor of the argument for Affinity being able to compete with Adobe if InDesign is in the top 3 Adobe products.