Mmmm. But the Quill itself if magical (and apparently contains a soul) and needs a special and specific person to wield it. The tree that turns into the wardrobe is magic but neither August nor the chisel are magical like Henry and the Quill. Even if August super believes in himself that still doesn’t change the fact that the chisel is just a chisel.
Correct me if I’m wrong but I thought August said the chisel was magical. He just didn’t believe he had it in him to wield it like his father did.