Adding enchanted books

So, ya know how you can add 2 unbreaking books and get unbreaking 3? What if you could do that, but with an unbreaking 3 and protection 4 book? It would be really simple; it's the same thing you do for something like unbreaking 2 and unbreaking 2 books in the anvil. you'd make an unbreaking 3 protection 4 book. It would just make it easier to get maxed out tools or maxed out armor. it would still cost xp to add them, but it would make it so instead of not being able to max out armor because it's "too expensive," would make it so it would only cost around 5 levels to add all the enchants to the armor, but still a lot of levels to combine the books. So now you can finally have no problem getting maxed out armor being it's too expensive! But you'll still need a lot of levels.