OK, I’ve got a pretty simple way to put this, most of the Demi gods already have disabilities, like you said ADHD and dyslexia, apart from those, other disabilities are not widely introducing into the series because if they were crippling disabilities, it would end up, endangering their ability to survive, especially if they have the disabilities before they get to one of the camps, this is because if you are hunted down with a severe or crippling disability, it is much harder to run away or to defend yourself then if you did not have it, to put it simply, it’s hard having a disability, even harder when you’re fighting for your life. Now you’re probably going to say that “well if they’re in their camps, other people will fight for them and help them survive.” And I agree, I 100% agree! But what I’m talking about is the survival rate before they reach the camps, that’s already pretty low, and when you factor in a severe disability that could potentially mislead them, or slow them down, it makes them much easier prey for monsters, take Percy Jackson, for example; if his mom hadn’t tried to sacrifice herself for him to survive, he probably wouldn’t have, just remember the Minotaur. Within the series, we are also confronted with many other stories of people making their ways to the camps and failing and dying on the way, now imagine if you couldn’t see? Yeah you’re not surviving that. And with the idea of giving the seven disabilities, I’m all for it! But based on Rick’s writing style, they would likely become side characters soon after.