I've never seen such an immediate nosedive. It started really high up there, and just decided to kill all interest by turning great looking succubi into children. No thanks.
I've seen worse manga continue on for ages. Though maybe this would've continued on if they'd speed ran the previous arc and got to this Dark Lord trial sooner.
Guessing the author is taking a page from Solo Leveling and has no real road map for the story. Things just happen. Except this author doesn't pull it off well.
MC: "There must be some way to measure strength..."
looks at park
MC: "I know, I'll kick a tree!"
MC spots a rock after kicking tree
MC: "Oh, I could've just kicked this rock.
later as MC passes a gym
MC: "Oh, I could've just kicked those dumbells."