Why Rachel's Hairbrush wasn't as useless as we think and how overrated Magnus's sword Jack is. And how powerful Alex's string is.
It did a lot more than u think. Rachel threw the hair brush and saved Percy's life. She also stopped the shaking of the tunnel which Annabeth had said she could not deal with. She brought Luke back to his senses for a few seconds. That helped him where as it slowed down Kronos take him over. It delayed it for a bit. Without her doing that Luke would have never been able tor regain his senses so he could stab himself and save Olympus.
The other weapons in Uncle Ricks books can cause damage and the wielder can be fine if in the fight they dont get hit. But no matter how careful Magnus is no matter what he will have to deal with the injury's Jack got where as the other weapons dont. So Jack might be powerful but he isn't the best weapon of choice.