That isn't Ego's MO (fragmebtation, pulvetization, what have you). Peter's path of destruction on Earth gives off a ton of radiation. Given that, and his proportionally insignificant power put on Earth, which is in line with what Ego has shown capable on his own planet, that wave of destruction is Peter going planet to planet, soearding across their surfaces with and letting off a ton of radiation, with a day.
Even still, Earth is not unique in having a seed. Most if not all of those planets should have a seed, which is how Ego is actually able to do his Expansion.