In my opinion, they should (to the least) up the durability of the next tier by 100%, and maybe lower the stone tier durability by 50%.
That way you have something which is "better" which breaks every time, versus something that's slightly worse, but that you have to repair once a day.
That's also kind of realistic, isn't it?
After all, it's like fighting zombies with sticks, or fighting them with a durable, full steel, machete.