You truly are daft.
Ok, so if any one of the pools from the largest to the smallest attempts a 51% attack the hashers who direct their hashrate to a pool that is not acting beligerent can very easily direct it to a mining pool that is not acting beligerently. Mining, and mining pools are the very definition of a fluid situation. What you are saying is like saying the ocean is not decentralized because there are only 7 seas.
Ok, so if any one of the pools from the largest to the smallest attempts a 51% attack the hashers who direct their hashrate to a pool that is not acting beligerent can very easily direct it to a mining pool that is not acting beligerently. Mining, and mining pools are the very definition of a fluid situation. What you are saying is like saying the ocean is not decentralized because there are only 7 seas.