Breaking Bad came out in the late 2000s and this was a time when being "politically incorrect" was epic - and by politically incorrect I mean just punching down and being hateful. Slurs for disabled people were used without any meaningful pushback, and at least in my experience, kids were happily reciting lines from South Park and Family Guy at school and mocking kids from SpEd classes. These things still obviously happen today, but now there seems to be more criticism of when it happens and even the "anti pc" crowd will hesitantly shut up if called out.
Anyway, Walt Jr. has cerebral palsy, but unlike much of the media of the time, he isn't the butt of the joke (aside from that one scene in the store but the bully got his ass kicked) or made cynically by someone who doesn't care or know anything about the disability to get a cheap emotional response from audience. Obviously he doesn't have an identical life to someone who is fully able bodied, but overall he's just a kid with his own angst and goals who just happens to be different. Sometimes he needs assistance, sometimes he doesn't. Sometimes his parents struggle to relate and help him (both for his disability and puberty in general) and that's just life, especially for a lower income family that doesn't have access to all the resources or free time to discuss problems.
I'm not surprised that they made :dean-malice: racist because he's a DEA agent, but rewatching it I'm surprised they didn't make Walt Jr. a caricature because most people wouldn't have bat an eye.
I remember being a little surprised when Walt Jr. gave his parents attitude or otherwise acted like a bit of an asshole. I was used to characters with visible physical conditions being portrayed as paragons of virtue, as though their purpose was to portray their conditions in a purely positive light, apart from the reality of the human experience. Walt Jr.'s condition adds to the story, but he's still a complete character without it. He's a good person, but not a caricature of upright morality.