On the contrary – with this population size. If you were to distribute the population outside of cities – it’d be much more harming to the environment. Unmanaged waste, unmanaged energy production, unmanaged food and so forth.
It is city design that harms the earth per se. That is, if cities were designed to manage waste better – turning it back into usable forms, Reducing their effect on the rest of the environment. Also the behaviors and choices of the citizens mind you. But otherwise, we’ve to live too – and we’re many. I can’t see another setup work aside cities.