The story was practically finished when Naofumi had his proper vengeance towards the royals that wronged him. What was their name, Bitch and Trash I think? Originally, the Call to Adventure in this story was the fact that Naofumi was treated unfairly and the story was basically a revenge run revolving that event in particular. That story was finished by chapter 32. Frankly, mr protagonist here has reached his personal goal.
Everything past that point are, from how I see it, attempts at making the publishing to last longer since the demand was there. The vassal heroes, queen whatever-that-bird-was, the beastmen slavery, etc despite being mentioned since the start, doesn't have anything to do with the protag's own story. How can they be? Naofumi's already got his vengeance. Abolishing beastmen from racism and slavery or making sure the bird becomes a the next bird queen or whatever wont help with Naofumi's revenge at this point. It's a nice cop out for authors since it makes the story non-commital and when it stops selling they can just end it at whatever the hell the tacked-on arc it's on.
As for my "tangly" statement, yeah the author is just trying to pull multiple "actually, (x) character was
" in order to make the story more than what it actually is. Feels cheap and not properly storyboarded.