Remove Banner Duplication

By default, custom banners can be duplicated onto a blank banner, either with a crafting table or inside the players 2x2 crafting square. I'm trying to remove the ability to duplicate banners, while still enabling banner crafting with loom. I've made a couple simple datapacks in the past, but nothing I'm trying is working. My first idea was to make banners non-stackable, which should remove the ability to dupe them. Either the idea isn't functional, or my pack isn't working. Any help is greatly apreciated!