Here's how gunsmithing/crafting could work without killing the endgame.

  1. remove legendary drop completely.
  2. bosses can now drop legendary schematics at decent rates (20% maybe) bosses can also drop very rare (less than 1%) trophy gun that deal 0 damage and exist solely to show off. EDIT make schematics single use like you need to burn the data storage or something when putting in into the crafter
  3. when you disable a gun for parts, you only get to keep 1. This means you would have to hunt down every single parts of the gun throughout the world while also getting casual players the ability to swap out the scope/sight they hate on the good gun they just looted in nm