Truth be told, I get the impression that there's a tug of war going on between the author and editor over what the series is. It feels like the author would rather do mahou shoujo in shounen superhero dressing with SoL chapters and a huge focus on emotion over action which is basically what it was prior to the ninja arc and makes sense given that the author clearly likes mahou shoujo. Even the fight with Sveta and Kfufu wasn't all that long, certainly nothing like the Hollow arc which is literally half of the series' chapter count.
The editor/publiser, meanwhile, probably wants it to be "more shounen" and as a result we get... the Hollow arc. Which had lots of good stuff but was also dragged out interminably with a larger focus on action over emotion even though most of the best parts of that arc (Spirits and Kfufu, Meng Long and Thumping and their masculinity debate, Mai breaking free of her guilt, the ending) were the ones focused around emotion, not action. Spirits sitting down next to Kfufu is a way more powerful and memorable moment than all the stuff Shy did in her fight with Mai. The best of the action was probably Lady Black going berserk on Prayer but admittedly Pilse's my favorite character so I'm kind of biased on that front.
Also the result of this shift to being more action-oriented means the series is starting to suffer from the same problems every shounen action series does: the MC randomly pulling out new powers and techniques as needed and lower powered/non-powered characters getting their screentime dramatically cut since there's nothing they can do in long, epic battles. Obviously this has affected Iko the worst who's gone from main character and Teru's best friend to only getting a handful of cameo appearances in the last few dozen chapter but it's not just her, Unnie hasn't really been relevant since everyone went to the dome either.
Ehh, I think you are reading too much into it. This is the author first manga, it's very common for a writer's first work to suffer from pacing issues. Like, the Hollow arc wasn't even that action oriented, 80% of the "fights" is just people standing around and talking.
