@Bluehammer12
It's not really novel. There's at least one isekai story adapted into anime that has that sort of tone (harsh reality, nobody is overpowered), but I'll refrain from mentioning the title to avoid spoiling it (and because I forgot the title).
A decent amount of plot armor is important for an enjoyable story. I personally didn't enjoy the stories that were based on DnD sessions of the writer(s) where important-looking characters die with no buildup nor any tropes played. You know your character can die within an hour into the session due to one bad dice roll and it's no fun. Furthermore, if that manga/anime character was revived, or if another important character dies, then any following deaths would feel less impactful.
Not sure why you would expect that of this specific manga and not any of the others with more developed characters whose deaths would have a larger impact.