Results Of The Breakthrough
Deus would only be satisfied if he was at least invincible on planet earth. Although that level of power was still cannon fodder in the vast universe, at least that would be considered a minimum requirement for him to leave planet earth in search of his girlfriend.
If he wasn't powerful enough to easily defeat the current strongest on planet earth, then he wasn't qualified to leave planet earth to traverse the world outside planet earth. He would be overestimating himself if he left planet earth with his weak power.
Although planet earth was invaded by alien monsters from another world, Deus had already guessed that it wasn't something too major, or else a sentient alien monster would have already caused destruction on planet earth. So there must be a hidden powerhouse that backed the planet earth or the milky way.