I think the Traveler is the Darkness. Where is the damage on the traveler? Facing the Last City. If it defended Earth from something coming from the cosmos why would its underside be damaged. I think the Traveler destroyed all life on the other planets and then when it turned to Earth, Humans stood up and defended it, just stopping the Traveler from crashing into the Earth's surface. I think we created our own Golden Age and that drew the Traveler or as I believe The Darkness.