It's not that we don't think ADHD is a disability; it's that we're more convinced by the social modal of disability than the "there is just something fundamentally wrong with your brain" modal.
For me, it causes me a LOT of problems, but I think most of those problems are looped around each other and exaggerated by society, and by the resulting secondary, problem-compounding problems that tend to pile up on top of adhd like depression, anxiety, cptsd, low self esteem, poor diet and sleep, and so on and on.
I see it exactly the same way I see autism. Not fundamentally bad, even though it absolutely causes issues. Autistic people, for example, run into heaps and heaps of trouble because of the difficulty they have communicating with more neurotypical people. They might miss subtle social cues and be ostracized, or be very direct to the point of being seen as rude, and get ostracized or fired from jobs and so on.
Meanwhile, off meds, I miss subtle social cues because I can't always look at someone's facial expressions and talk at the same time, and maybe there's a song or an anxiety loop or a previous conversation topic stuck in my head. Or I can't talk coherently because I think of a whole wordcloud of an answer all at once and can't pick a linear route through it fast enough. It's not so different, imo. The reasons are different but the resulting problem is the same, more or less.
And both ADHD and autistic folks experience sensory issues.
I suspect if there were meds that helped autistic folks the way meds can help many adhd folks, people would probably view it more the same way. Or if ADHD meds didn't exist and we just had to exist without them.
Even as it is, autism is so much more stigmatized than unmedicated ADHD. If ADHD is an illness, and autism is not an illness but is a stigmatized but normal brain difference, why do autistic folks usually seem to have the harder time in the world? Why is society's shitty response to adhd "ignore it, it doesn't exist", while its shitty response for autism is to widely adopt a child abusive "therapy" invented by the guy who invented gay conversion "therapy"?
I get tired of the people insisting we don't have huge struggles or count for disability help, too. But tbh I also get sick of being told my brain is broken and that my adhd is an illness, because I don't think mine is. I think it's just different, albeit in an often very inconvenient way. But I see upsides to it too. I don't think I would trade-in for a neurotypical brain, to be honest, despite all the problems. I like the creativity and the non-linearity of thought and the outside-the-box thinking and the hyperfocus adventures. I like my neurodivergent friends and the way our socialization works amongst each other. And I do have the meds, which help a lot with the problems.
For my, and my own adhd, it's both a positive neurodivergence and a disability. Not an either-or.
All that said, I kinda don't think "neurotypicals" per se actually exist, especially when accounting for the really dramatic plasticity of even adult brains, and the way experiences and thought patterns can and do continually change the structure of the human brain. And ADHD folks share symptoms with a lot of mental illnesses that aren't considered neurodivergent normally.
Talking about neurodivergence is helpful because it's a more positive and less medicalized lens for looking at things, in my opinion. I like it. But the neurodivergent/neurotypical binary idea can also become a problem.
Anyways. Different peoples' experiences with adhd can differ a lot. If you see yours purely as medical disability, that's a-okay with me, and you don't have to describe yourself as neurodivergent, but I don't see mine that way.
Perhaps on all sides of this we could benefit from being more careful not to describe other peoples' adhd in authoritative tones based on our own. Like, I agree not to call your adhd neurodivergent, and you agree not to call mine an illness? (Tbh I think you did a good job in your post of talking about yourself rather than talking for others.)
/ramble I half-feel like deleting and might later but at this point I've committed too much so here you go I guess
Edit: also there's so much overlap between autism and adhd I've heard some talk, sometimes, about whether they might be best classified as two forms of the same thing. shrug The science is still sciencing on this one.