User blog comment:Zathronas/Analysis by an author: Part 2 Antagonist, the Darkness/@comment-3387274-20131219202133/@comment-12227301-20131219204824

The "Grimm are actually dangerous" bit makes sense. But there's still the issue of having to chalenge those chosen protagonists, who are also rather weaker than their fully-trained counterparts (and fully-trained selves). It's true the grimm could be the greatest threat humanity has faced as of yet, but it can't be the greatest it will face, or the cast will just mow down legions with one hand by the time they end their second year (exagerated, but you get the point).

If the select few can struggle against them before growing, humanity will always be chalenged by them, but the protagonists won't.