Wait, wait, wait, hear me out. Wrench Wand and Cautery Sword are both dead-end low-level weapons that appear to be effective against a specific family of monsters, but are generally outclassed by using the proper damage type. Similarly, Cold Iron Carver has a damage bonus against a specific line, but builds all the way to five-star, and is built from an easy to use sword (that you get for free).

So here's the gist of it; both Wrench Wand and Cautery sword are moved to 4-star, build from Tempered Calibur, get a 5* upgrade (I'll call them Deconstructor Staff and Surgical Sabre), and have the same damage levels as the Cold Iron swords.

Additionally, I'd like to suggest that these three swords have their damage bonus expanded to include both monster families that deal the same damage type. Cold Iron Carver would slay shadowy fiends as well as undead; Wrench Wand would dismantle constructs and clobber their gremlin masters; Cautery Sword's proficiency at cutting organic tissue would be as effective on beasts as it is on slimes. This would make the weapons useful for monsters likely to be seen together, or would let newer players chose a weapon based on the damage they're likely to receive (instead of picking a damage type that might be a dud, like fighting gremlins in a machine stratum).