That’s true. With the other characters with disabilities, either they weren’t born with it like with Tavros or the disability was implied like with Sollux. So yeah, that does suck a little for having the main villain be the one with a stated mental disorder.
But we can’t say that Hussie did a bad job or wasn’t trying either. He gave at minimum 20 diverse and fleshed-out child characters with various abilities and disabilities, canon gays, intricate personalities where if you don’t like one, there are like 12 more characters to love.
Plus, it wasn’t like Caliborn is evil because of his learning disability. Hussie made that line clear that Caliborn being evil is because he is a evil little kid who likes violence and murder. Disability can happen to everyone, good and bad, and it sort of normalizes it where it is just a thing with no affect on personality.
I don’t want to go Kankri here, but I am a cis white woman so I don’t really have a view-point on what it is like to not have representation. If the stuff I say here, or anywhere on my blog, is offensive it is because of ignorance on that front.
So I guess what I am trying to say here is, because of all of the characters like Sollux, Tavros, Terezi, Aradia, Karkat (etc) that Hussie wrote, where the disabilities are a part of them but not defining them, I didn’t even blink when Caliborn said that he has one as well. It was just another part of him.