@mismarca
I think the issue regarding the new characters is that the release is so damn slow it's painful. It appears the translation pretty much caught up to the raws and the manga started 5+ years ago.
Now imagine how long this could keep going before a satisfactory resolution.
I've read the 57 chapters in two sittings after having dropped it couple monds back, and the only reason I managed to finish it this time because the characters were somewhat interesting.
At this point every new character is just fluff, even the song girls were just there for their arc and now while the "sister" has a token spot as moss researcher the other one didn't really have screentime since the spanking. With only 1 chapter a month the author doesn't have enough time to flesh out the whole plot and every character. I think he is going for some super complex story with many powers and interests fighting for the "power of the evil god" as a tool, the MC is kept as the typical milktoast isekai character because if he developed serious character traits the story couldn't progress.
Imagine the MC had his own opinions and desires (aside from muh Sun and be friendly, nice and help people) then he could just do whatever he wishes, fight for a side he chooses and go on.
TL,DR:
I think the author tried to write something about many different interests fighting for control while the MC is just a tool to help the readers get acquainted with the world and the "actors of the world".
Essentially turning him into nothing but a force of nature, a really bland one at that.