@ShadenKnight I (and perhaps others) dislike the isekai genre because it has truly become lazy wish fulfillment copy-pasted. There are usually only minor, superficial hiccups that get in the way of the protagonist and on the flip side the protagonist habitually manages to solve multiple problems at once with expediency (the laws of convenience usually bending itself to allow the protagonist to do so). The protagonist is never challenged, he never doubts himself, he never questions if he's actually in the right; he just keeps going and going blithely. It's masturbatory, and if I wanted that, I'd just go watch actual porn.
"Souma is only as smart or seems that way because he was sent into a medieval fantasy"
Is there a law that says medieval fantasy people are automatically stupid? Even if so, they are stupid in a way that automatically favors Souma? If they're so stupid, why don't they just deem Souma as crazy or torture him for information? There are a lot of ways to be stupid, yet it conveniently results in Souma becoming king. Think about that for a second. So these medieval fantasy people are automatically stupid, but they're also just smart enough to abdicate the crown to a guy from another world because he may or may not be just making bullshit up. It strains the suspension of disbelief.
My point on the demons was simply repeating what the chapter itself said. I don't know why they stopped their invasion, the chapter didn't give the reason why, and I don't really care. I'm also willing to bet that, as is typical of the isekai genre, the poor demons' circumstances led to them invading the human world, that they're people just like you and I, and that they could all get along if they just forgive and forget!