The whole idea that only debris of his home planet would weaken Superman is kinda hilarious. I mean... why?
Kryptonite is something that was created during the destruction of his home planet. But it's a material that's created everywhere in the universe every time a star explodes. So the Kryptonite found on Earth is not from Krypton. Or something.
Perhaps the creation of Kryptonite is dependent on the radiation from Rao coming into contact with the radioactive elements within the debris of Krypton itself, like Kryptonian rubidium coming into contact with gamma rays?