a little far fetched, their purpose of using earth is to create bio-weapons for their war efforts. They had no qualms about squashing a failed experiment, ie the dinosaurs and they have plenty of time to let their experiments reach critical mass.
they had assumed that the experiment with homosaepians was successful but discovered that free will is dangerous thus decided to cut their losses and squash the experiment again.
if they did come back to earth or to this galaxy again and discover that their abandoned experiment has endured they might take a interest in finding out how things has progressed without their supervision and intervention. But helping Archanfel cos one of them felt bad isn't going to be high on their list of things to do.
If the ark's launch gave off an energy signature that alerted them to this galaxy, the first response would to be observe and then launch the meteorite attacks again. Nothing in Chronos' arsenal besides the Ark can defend against a wave of meteorites. Two "ultraman" or not. That apocalypse is not cancelable.
