The delving bench is one of the most infuriating examples of RNG gating on Siptah. You need to spend 20 eldarium bars, i.e. 40 decaying eldarium, i.e. half of what you get from a vault whose final chest isn’t bugged, to get one chance to pull the slot machine lever and see if you’ll get a recipe you want.
On average, it seems to give you a recipe every 2-3 tries. There is absolutely no way to influence which schematics you’ll get for a given item type and the schematics you’ve already unlocked don’t affect the outcome.
As a result, if you’re trying to get a specific recipe, you’ll end up with many duplicates.
My suggestion: allow us to put the duplicates, along with the item and the eldarium bars, into the delving bench, and have the bench potentially consume them too (as long as they’re of the same type as the item). They wouldn’t affect the chance of getting a schematic. If you don’t get a schematic, they’re not consumed. If you do get a schematic, they’re consumed and affect which one you would get – none of the schematics that you put into the bench would be eligible.
For example, let’s say you’re aiming for the Scepter of Unclean, and you already have the duplicate schematics for the Bonebreaker Mace and Gravebane. You put in 20 eldarium bars, a star metal mace, and those two schematics. If the delving bench decides to give you no recipe, you get a broken star metal mace and those schematics back. If the delving bench decides that you win a recipe this time, you get a broken star metal mace, and a new recipe that is guaranteed not to be the Bonebreaker Mace or Gravebane. And, of course, those schematics are gone.
It’s still grindy, it’s still a slot machine, but at least it doesn’t make you want to flip the table…