Even though it's kind of beside the point since they were trying to reform the world through peaceful means, trade (mutual dependency for greater prosperity), and general development for greater quality of life, it's still true Hero is way too OP. With such a character the only choice left is to either keep him away (like he was now in the demon realm) or force the story to follow non-fighting solutions even when they would appear unlikely. That's clearly careless character designing considering this is a story where potential for wars is so huge (because the nations have been solving pretty much every problem with warring so far).
That was kind of the point though, a lvl 100 Hero's power doesn't amount to much when striving for the peace they wanted.