I get why people don't like the arc since in the black and white demon author pretty much drop a big bomb but the arc after that doesn't explore it and instead do Idol thing, but IMO this arc is important since it's a breather before the next bomb being drop, and it flesh out the classmate character, so it's not like a certain hero school manga where they didn't flesh out most of it's characters even tho it's already past 300 chp.