ADHD is a valid disability.
Our brains are so fundamentally different that our brains have a completely different neurological development style. Our brains process information differently, interpret stimulus differently, regulates itself differently, is chemically different, is physically developed different. The frontal lobe of a person with ADHD is physically identifiably different.
ADHD affects everything from how you hear, what you remember, how you read, how you eat, how you structure sentences, how you hold objects, how you process emotion, and the behaviour you express during interaction others. ADHD affects so many categories of functioning as a person.
Here are a collection of helpful infographics
https://tfw-adhd.tumblr.com/post/630767903104532480/diagrams-showing-overlapping-symptoms-adhd-and
