It's been like that for a while (like "anti-idols"). Japanese media is always unpolished and cheesy anyway, which is one reason anime is the only part anyone outside the country cares about, but the music industry does have a surprising amount of room for letting artists do whatever they want as long as it works.

When I heard about Atarashii Gakkou I thought it was some kind of American fan group because the name sounds like it was Google translated… guess it's just unpolished too.

I'm not sure if the unpolished aspect is intentionally produced or genuine. I would bet on the former, that...they intentionally take idol quality girls and go plain on the clothes and makeup for that "girl next door" look.