The Series Deconstructs Several Common Anime Tropes by Showing How They Would Actually Appear in the Real World
It's noted on the Big Eater page that Hei's appetite is somewhat jarring given the series' fairly serious tone. However, I'd argue that besides the likely in-story explanation because Hei was "fused" with his sister, he is "eating for two", it was a deliberate choice. Besides the fact that being a Big Eater does seem to be a common attribute of characters who use Obfuscating Stupidity (e.g. Vash in Trigun),it is important that the way such characters eat, as well as Hei himself is at odds with how people act in reality. The same could be seen in April as an example of a Hard-Drinking Party Girl. She behaves towards alcohol similarly to countless other anime characters, but her take on it- "someone literally powered by alcohol"- takes the trope to an extreme.
In a similar way, although it doesn't seem like she was intended as creepy, and thus seeing her as moe or at least sympathetic wouldn't be Misaimed Fandom, the way in which Yin became an Emotionless Girl, being essentially Mind Raped by the Gate, makes the trope unpleasant. This also emphasizes that there really would be something wrong about a person who was fundamentally lacking in a emotions, and even more unnerving, is that Dolls aren't even treated as sapient.
Finally, I'd note how the series plays with the Innocent Fanservice Girl trope as well as some of November 11's mannerisms. Although used in fiction, someone who lacked a nudity taboo in reality, or treated macabre things as lightly humorous would be considered odd at best, insane at worst. It's no coincidence that all of the tropes mentioned characterize Contractor or Doll characters, underscoring how they are parodies of normal humans. Thus, the message sent is that even if such behaviors are common in fiction, they would be unnerving if encountered in reality.