This arc feels like the author had an idea for another manga and decided to shoehorn it into this series.
I mean, this flashback feels like it's feeding back into the main story? One of the current unknowns for the story is their religious pantheon. The Saint is as much a tool of the Gods, as the gift they send the Divine Implement. Freya, Lotus, and Edelweiss were all Saints, which was epitomized by the Tool. But, we've never actually seen them, or even know if they're "real". Whether or not Freya and/or Lotus was betrayed(and thus possibly also Edelweiss), the Pantheon that empowers the Saint is a big part of their fates.
What I've personally questioned, is Chapter 37 Page 15, what happened to the Prime Minister. That's not normal human physiology, Calmia said he was just a puppet. But puppet of what? It felt like his personal animus towards eradicating the demons was to aim for Human/God Supremacy of the world. And if it was the "gods", is that tied into what's happening with Takeru/Takeru. So whether or not it's been shoehorned, there are still unknowns that have a deeper lineage.
And this flashback, probably ends in the next chapter. Since you have Cardinal growing up, and then the tragedy that caused the current situation. So, after that you head into the conclusion of this arc, whether that's a god coming back from the dead, Waifu Cardinal, all the Earthlings being ejected from this "Utopia", and/or anything else, you have a bit of backstory of the world building that the author is trying to do.