The whole point is that RSA and ECDH can't be made safe against quantum computers by making the keys bigger. The speedup is exponential and so breaking a 4096-b

The whole point is that RSA and ECDH can't be made safe against quantum computers by making the keys bigger. The speedup is exponential and so breaking a 4096-bit key is only twice as hard as a 2048-bit key. The 'cutting in keysize in half' is true in principle in general (but not in practice, as the article points out), but for some algorithms it's much worse.