Again we're experiencing things just as Kumo is experiencing things in the manga, all of the worldbuilding in Shun's side is essentially just to show how big of an effect Kumo's actions were having to the world. That's it, that's the "worldbuilding" you guys are complaining we're missing, The more important worldbuilding is on Kumo's side, the few on Shun's side is mostly towards the part where the 2 coincide.
Like the only main thing manga only people are "missing" is the teacher's side of the story and even that isn't really needed yet...