The paradox appears flawed by assuming a reference point remains in the same place over time. While a city on a planet remains in the same place on the planet, the planet and it's solar system continue to move over time. Five hundred years ago the planet may have been a light year away from where it is today in space time. To time travel, you would need more than this simplistic model to relocate to an earlier time and remain on a planet. It is not a static model. It is a fluid model.