As someone who has used the holy wrench on hundrends of slayer tasks I can say it would not be too op for the toolbelt. I don't know of any other pocket slot items I would use on slayer tasks except for vamp scrimshaw. Illuminated books are used to set fastest boss time records. I still don't see why it shouldn't be added to the toolbelt. If it really is too op they it shouldn't even get an upgrade.The brightest ideas are the most undervalued.