@Roadrunner9000 :
we seem to have very different definitions of the term superior
Almost certainly.
When someone like this says thy are superior, it is in the same way that the KKK, Nazis, etc claim they are superior to non-whites. Bigotry and racism born from (often false) pride, and has absolutely nothing to do with combat abilities.
The standard trope in for royalty/nobility in fantasy stories is to place social value almost exclusively on bloodline. Because origin and tribalism are pretty much how people work in the real world both historically and to this day. To many people still thin if you have lesser origins, you are a lesser person, or if you are not THEIR ethnic group you are an outsider and not to be liked/trusted.
A random teen from another world does not have the same level of pedigree as a noble from their world, so inferior. The Demon King is not human so inferior. It is so F-ing obvious that every time I read comments like yours, and the rest of the same drivel in this thead who said the exact same thing, I have to wonder are you just being a troll looking for something to complain about, or not aware enough to understand what is going on. Seriously who is superior between Steven Hawking and Mike Tyson, to many people in this thread are making comments that would mean it has to be Tyson in their minds, but in terms of contribution to society and lasting impact on the world it is Hawking by an insurmountable margin. Want a closer example to the story how about a Trust fund brat/heiress and the mechanic fixing her car, it could be the most expensive mechanic in the world but she would not think of him as anything more then "the help" and never an equal.
This is part of why these betrayal stories often need an isekai protag, a sheltered child from a peaceful and lawful country with a culture that emphasizes respect and obedience, which Japan is but many (including the USA) are not, is not going to question what they are being told and will be easy to manipulate into fighting for them, plus has no connections of background so is expendable and can be tossed aside on a whim once the job is done. Someone from that world would either have a strong enough background hat they could not discard him, or enough prior knowledge to know not to trust the princess, or any other noble