In the thread about crafting, a lot of discussion and controversy has been made about item durability.
This comment in particular gave me the idea for a way to impliment durability that would prevent this type of behavior, but still make epic items vulnerable to eventual degradation. As @olliepurkiss mentioned, durability is intended to make even the best items temporary so that really epic items can be made without being game breaking.
My suggestion is the “hardness” property, and it is based on the hardness of the materials used in creating an item. Hardness scales liniarly, from wood to stone, metal, alloys, etc. Hardness is basically an items resistance to durability loss based on what it is used against. As an example, imagine a stone pickaxe. Using a stone pick to mine stone, my pick takes normal durability damage, but using it to mine sandstone, which is considerably less hard, my pick takes about (arbitrary value!) 50% durability damage. If I upgrade my pick to metal, now stone only does 50% durability damage, but sandstone does less (perhaps, 0-25%). If I upgraded to vastar pickaxe of doom, now I can mine that stone that is in my way at little to no risk to taking durability loss, but mining more materials to make new doom picks does normal durability damage. In this way, you don’t feel like you’re wasting your best materials mining common materials, but you can’t use it forever to mine higher quality things.