When importing products from a supplier catalog, the data for that products categories already exists. There should be an option to include that data when copying that product to your catalog. The "Copy Product(s) To My Catalog" section is already built as a dropdown menu but only holds that single option. Adding an option that says "With Categories" would allows users to choose whether they want to copy that product over with no categories assigned or with categories assigned.

This makes it a lot easier to build out massive stores with hundreds or even thousands of products. Having to manually assign all of the categories to that product takes so much time.