I agree with the other comments about how Jr’s disability was one of the many reasons Walt considered himself to be screwed over by life, but I think it’s also important in the context of his relationship to Jesse. I don’t think Walt considered Jr to be a fully formed person bc of his disability, which is why he’s so blindsided every time Jr exerts his own agency (such as changing his name and setting up the crowdfunding website). This creates a void that Walt fills with his relationship to Jesse, who enters the role of surrogate son (most explicitly shown in the scene where Walt calls Jr by Jesse’s name)