Honestly Dr.manhattan was kinda dumb. “Oh I need to stop humanity from nuking itself” meanwhile I demonstrate easy ability to travel to other planets.
Doctor Manhattan's ability to save the human race wasn't the issue. He was basically a god. It was his willingness. He didn't feel the need to stop humanity doing anything:
A live body and a dead body contain the same number of particles. Structurally, there's no discernible difference. Life and death are unquantifiable abstracts. Why should I be concerned?
For All Mankind is the Star Trek prequel we should have had. Co-created by Ron Moore (Deep Space Nine, Battlestar Galactica), the show has a bunch of Trek alumni working behind the scenes. It features human drama (and sometimes melodrama), geopolitical diplomacy, sweeping cultural change and scientific adventure against the backdrop of a multi generational future history, starting with the first moon landing.