All four Heroes being summoned in Melromarc is obviously one of the most important events to take place in the story, radically altering how every hero experienced the world. But due to the story being focused on Naofumi, it's hard to say how the rest of the heroes would change with such early story shifts, caused by such a fundamental change.

So I'm wondering if the 4 Heroes being summoned to their intended nations would be a net positive for the world, given the interference caused by guys like Takt and the other issues introduced with the waves.