The problem with this movie is that it shows people barely surviving in this world of monsters, when it's not even the case. The people have always been living in tandem with the monsters, studying about them and learning how these creatures live and thrive, while also making progress and develop culturally.
Also, the monsters don't just mindless kill anything they could grab their claws on. They're similar to animals, in which they understand the concept of territories, utilizing their surroundings to their advantage, as well as knowing their own limits.