I think this is a good example of how we mix up concepts: ADHD is just a phenotype. Then, our society classifies it as a condition because it does not go well with current circumstances. Although, both are separate things.
No it's not. It's a disability with very serious consequences for the lifespan of people affected. Please don't repeat this pointless pseudoscientific bs. This link contains a good starting point to understanding what science knows about it. https://www.sciencedirect.com/science/article/pii/S014976342...
I eye some risks people with ADHD have, like higher risk for STIs. Sure, Russel Barkley things people with ADHD getting STI's makes them "disabled", but evolution gives a bit two thumbs up to people with ADHD having unprotected sex. Barkley then brags treating ADHD will reduce STIs, by you know, reducing the amount of unprotected sex with multiple partners that they're having. If anything listening to Barkley's advice is likely to make the average person less reproductively successful.
I don't know, I don't like Barkley and his pro-pharma fan club. It's correct that medicating people with ADHD will profoundly change their behaviour. But I don't see any reason to call the prior way people ADHD people behaved as "disordered" and "a disability" and the new way they behave on stimulants to be curing them of a horrible disease or whatever. That description is not scientific - it's subjective what we do or don't consider a disability or disorder. If you prefer life on addy, good for you, keep using addy. I find the entire way we decide to describe behavioural and neurological differences as disabilities and disorders to just be thinly veiled bigotry often taking the form of self-hatred.