I think the issue is manifold here, specifically.
Thinking on it more now, the trope of "totally unaware & idiotic protagonist" works best in an episodic series, where each chapter (or group of up to 3 or so) are self-contained, with no overarching storyline or professed character arcs/goals. Like a Slice of Life-type series, wherein we see the day-to-day of the characters getting up to this or that, but the focus is on their interactions and the quirks of their characters carry the actual narration. But there's few, if any, overarching narrative elements, no real long-term goals or aspirations, or "true continuity". Once the chapter's over, things reset, and we get a new episode of zany nonsense the next go-around.
Also, there tend to not be such clear distinctions between overt antagonists and benevolent characters. If there's a malicious member of the cast, they're recurring, and tend to be "low-stakes" enemies that are defeated, then come back around to try again the next time. The tension of the chapter is resolved by the end, and things then "reset" and the school bully or supervillain tries another wacky tactic only to be shut down again and again.
That's not what's happened here; we have a clear setting with multiple characters striving toward a specific goal, with actual malicious forces--now including humans on top of monsters--and the protagonist has a clearly stated goal that requires a progression of character and a growth of character to see achieved. The bad guys are the same, and the secondary & tertiary characters do, as well.
All of that assumes that we should be seeing real velocity to what's going on with each character that's been introduced. This is not an episodic series; there's progression of time and events, there's multiple chapters dedicated to a single incident, there's before-and-after states to the world setting due to the actions being taken.
We are only 9 chapters in; in real-time in-universe, it's not been much time at all, with few interactions between Kino and other characters to really lay the groundwork for what she's now experiencing having left her hometown.
In light of that, it makes sense that she's this dumb and oblivious. I would argue that some level of situational awareness to one's surroundings would be appropriate here - she grew up in a hellscape, where being blind to what's happening around you can mean certain death, and understanding risk, should be important facets of her character.
But if Kino's convinced that people can't be evil, then that's a valid-enough argument that I can see it getting to the point she'd allow herself to be tied up on a cross beside her friend. I think it stretches credulity because, again, she should have some amount of situational awareness having lived where she did, but that was monsters, not people, so I'll give her the benefit of the doubt.
However, this arc has gone on for multiple chapters, now. It's a gag-forward manga, and there's already been several facets to both the narrative and the layout of the manga itself and the characters therein, that go against the established "formula" of such a story.
So while I think it's prudent to withhold judgment on the series' potential because we are seeing the first "real stakes arc" of Kino's integration into society and the start of her professed character arc journey, the outcome of this--and whether or not Kino sees any growth on the other side and understands what she got wrong and learns from it--will be telling as to whether this series is trying to do two very different things simultaneously, and whether it can manage that.
Because a progression-style story that seeks to have its characters achieve long-term goals and see an actual change to the setting and state of the world after the narrative has concluded, cannot carry gags like "dumb & unaware protagonists", because the entire setting has to bend around allowing them to stay dumb & unaware--to the extent that it breaks immersion with side characters remaining forever silent about the truth around the protagonist, enemies getting one-shot with no change in awareness of the protagonist over why it only happens for them, and if that's allowed to go on for too long, it becomes harder and harder to justify in-world or in a meta-narrative sense.
So I think it's fine for now. But the conclusion of this arc, and whether anyone tells Kino the truth or Kino figures it out and learns and grows as a character, will in my opinion be vital as to whether the series can carry the gag elements successfully in the long run.