I was annoyed at first too, especially since it had technically been done before with Korisu's debut and the dungeon/Ninja Warrior thing among others. Actually thinking back on it, this author is a big fan of "instanced dungeons" as a setting. Some kind of area that exists separately from the outside world or at least the city.
But it's actually kind of a trope in mahou shoujo series. With Madoka and Daybreak Illusion being my earliest introduction to the genre, I can clearly remember so many of their fights happening in some sort of hidden realm. With that in mind it's not such a bad thing, it's just the execution that's a little off. Granted, this story has always had an unapologetically breakneck pace.
It was easier to reread this chapter when I understood that this was actually a setup for really good interactions and introspection later on though. This author might be blatant but their planning ability as far as characterization goes is pretty damn good so far.