The robots are busted and suffering mass errors, the moon people were the abandoned souls of the worst of humanity, and the professor was nihilistic as hell.
And that's just it, isn't it? Compounding onto everything Phos suffered through, their only exposure to humanity has either been through its worst reflections or through second-hand accounts.
Say what you will about Phos's current outlook on humanity, but it's only ever been inherited from others, and it makes sense (for them) at this point in the story.
What's yet to be seen in these final 5(?) chapters ahead is what the contrastingly optimistic and innocent life forms will take away from all this and how that will in turn affect Phosphophyllite if they truly are meant to oversee them into a new Era. Seeing as how it only took a few assuring lines to make Phos go from having a meltdown to being chill af, their influence is potent.
You could very well be right that we're just spinning our wheels here, but I'd rather wait for the resultion to this whole dilemma before coming to any conclusions personally, and Phos' willingness to still acknowledge and share the goodness in humanity, no matter how cynical they are, is something worth taking account of.
To people who wish the story just ended a few chapters ago, I honestly would've been kinda bummed that we never got this level of honest introspection from Phos that I've been wanting to see since vol 1 and onwards since, for most of the story, they've only been finding self-worth in appeasing others whether it be the other gems or the Lunarians.