It's not just an Oriental author problem either; I've noticed a lot of people who do this issekai shit tend to fall into the trap of making everyone a lot stupider than they realistically should be. It just happens a lot in Japanimation because they LOVE the genre. If you ever want to torture yourself and read either fanfiction/anything published on Royal Road, you can see a ton of stories that are just self-inserts with an author trying to be smarter than they actually are. Harry Potter's fandom had a whole subgenre called rational fics, where the MC was supposed to be super smart and above the setting's superstition and supposed stupidity, but it just comes off as Reddit atheist slop.