I agree partway with your point. Kind of like how Rick & Morty's authors, when people were overanalysing everything, they just said "people, sometimes a joke is just a joke"; not literally everything needs to have deeper purpose. However, two comments on that.
1: My main beef with Akame ga Kill was not that characters died without powerful motifs or plot-shattering events, but rather that the show ended up becoming a deathfest where death no longer had much value, neither by meaning or by shock. There's such a thing as overdoing it, basically. In the end, I stopped getting attached to any characters at all, cuz it felt like the author would simply kill off whoever he felt would be most shocking and traumating.
2: In the case of Goblin Slayer, it's not so much overdoing it as it's being unnecessary. One thing is showing how monstrous goblins are, and the reality that in gritty fantasy (and kind of in human history?) women in the middle of violent conflicts gets abused and raped by "monsters" if they are caught in the middle of it. That was done in the first episode, and to the people crying that such things are gratuitous I say "you are buffoons who mistake gritty and dark with edgy and foolish". Those scenes were good to establish the world and plot. But repeating the rape-related scenes in subsequent episodes would be nonsense. The ultraviolence cannot be skipped because it's the pure resolution of the conflict between the GS and the goblins, it is by itself its own purpose. But showing more rape tells us nothing about the monsters, or the characters, or the world. It would be juvenile, and simply the author/team revelling on showing us guro porn.
The dogma that you disagree with is less smth the anime fandom believes and more of a tenet in story writing. Absolutely every single scene in an anime has a purpose or meaning, even if that is "showing a girl's panties in an ecchi" or "establish that the characters are travelling by horse in an adventure". Goblin Slayer's ultraviolence sustains itself as its own mark of the house, but the rape "sub-plot" would simply fall short of any explanation other than "we want to arouse people with heavily-implied monster rape". At least, I believe (all of) this.