The entire TADC situation brings an interesting nuance to an old theory of the Internet - the one that the lighter/nicer/fluffier/gentler the work, the more awful, toxic, violent and nasty the fandom ; whereas fandoms of darker, more sinister, harder works tend to be more reasonable, understanding and well-balanced.
This theory is no news - it is an old idea that relies on the way fandoms have behaved when it comes to works of horror for example, or dark brutal war stories, or dark fantasy, or similar works ; versus cases like the infamous Bronies, THE definition of what happens when the fans of what is supposed to be a simplistic, goody two-shoes, nice and fluffy and light-colored children entertainment become a massive, nefarious, vindicative, petty and disturbed organized mass of adults. (Or at least it used to be, I don't know how it evolved since).
The dialogue was still up to date with the more recent case of "Steven Universe", which also became known for its toxic fandom (which for some became THE toxic fandom by definition) despite the story (while definitively darker than "My Little Pony" for sure) still being a relatively comedic, hopeful, "positive" show with colorful designs, feel-good messages and overall trying to be "nice".
But the way the exact same toxicity has gotten to a show like "The Amazing Digital Circus", which is definitively more mature in content and more anxious, sinister in tone, I think brings the nuance that this phenomenon isn't just about "feel-good kids shows". It is about any show that happens to look like one. Even if the story is dark or brooding, even if it is horror, even if it is about complex or sinister characters, as long as the show will have colorful design, as long as it will have a "kid-like" aesthetic, as long as it will have a "nice entertainment" vibe in art direction, the toxicity will raise up in the fandom.
Mind you, this is nothing proven - experiments and studies have to be led. But I believe what we thought before was wrong. It isn't that simplistic, optimistic, nice, "gentle" soft stories attract nasty, disturbed, violent people in the online space - it seems to be purely a question of aesthetic, of them swarming to colorful designs, cute styles and childhood-associated/nostalgia-bringing aesthetic.
However, to all the points above, I have to add two cases that muddle a bit the waters - the Miraculous case and the Helluvaverse case. The Miraculous case is definitively something similar to the My Little Pony case, or rather between the Pony and the Steven Universe case, as it is about a fandom taking way too seriously and in a way-too-complex style a show that was meant to be children's entertainment for PRIMARY SCHOOL KIDS. Because it looks good, because it has 3D style, because it was shared internationally and features teenagers, a lot of people assumed it was aimed at teenagers and young adults, but as I like to remind people the show is literaly put by TV channels in the same batch and hours as Paw Patrol (hence why it has a whole dozen of episodes dedicated to selling toys).
The Helluvaverse in turn is definitively a show for adult, by adults, about very dark subjects and other a lot of dark humor - gore, sex, etc... But it also has this more simplistic and colorful design, with a throwback-style that can potentially evoke the same "old cartoons" and "kids show" people are used to... But the more important tie between the two works is that in both cases the creator and showrunner got A) too much and too directly involved with the online fans and haters and B) clearly belonged to a generation or a type of people that is not used to the traps of the Internet and not ready to face the trolls, drama-makers, and people who are not their target audience. Thus a lot of the debates, drama and storm around their show was partially fueled by the creators themselves, who "fed the trolls" to the point you could say it was over-feeding.
But I think these two cases, of Thomas Astruc and Vivzipop's interaction with their toxic fandoms (and how it further made it more toxic) is to be compared with the way other creators have been dealing with toxic fandoms directly on the Internet - from Steven Universe to, more recently, Gooseworx, where in this case Gooseworx not being as "problematic" as Astruc or Vivziepop, and their case being one of a person that a mob on the Internet set out to destroy and managed to complete gut out (spiritually and morally speaking).
This post has no conclusion and goes nowhere, but there's a lot of comparisons to be made, a lot of studies to perform, and a lot of recurring things to consider.
EDIT: Oh yes I forgot to add - the only "nice, fluffy, cute" styled cartoon that seem to avoid the toxic fandom thing are those whose content truly, REALLY goes hard on the dark and makes it clear the target audience is meant to be enjoyers of horror comedy and black humor. I am thinking of Happy Tree Friends for example.
Maybe this is why things like Hazbin Hotel and the Amazing Digital Circus still attracted the toxic fandom so much despite going darker than things like "Steven Universe" (well at least early Steven Universe, it does get darker later, as all cartoons of this era did, slowly building up the maturity), because while playing on dark humor and horror comedy they did so with likable characters, optimistic conclusions, positive character growth and other "nice" messages. As opposed to stuff like Happy Tree Friends, which are clearly telling their audience "Hey, come see us if you want gore, horrible death, a lot of awful pain, and cosmic disturbingness... But it's cute!"