There are a lot of unrealistic aspects in isekai anime, manga, manhwa, webtoons, and more. The very idea of getting 'whisked away' to a new magical world where you get to do things over again and have cheat-like abilities is already unrealistic, but there are also a lot of smaller things that are unrealistic as well. The fact that these protagonists get so much done with just a few people is pretty absurd, for example, even with their overpowered abilities.