Disclaimer: I have no quarrel with the mods using the term in the creation of this community. I understand why they chose it, as even if they share my disagreement with the term when applied to ADHD, there's not really a better inclusive term. "Mental illness" is really the only other option, and naming a community that would probably invite darker discussions that the mods might not be prepared to handle.
Another disclaimer: I think the term is perfectly valid when applied to autism, as autism is not, to the best of my knowledge, a mental illness so much as a difference in processing. Being autistic is only "bad" in the sense that our society discourages autistic traits. (Apologies if this is wrong; I'm neither autistic nor especially knowledgeable about autism.)
The term "neurodivergent" implies that there's nothing wrong with you if you have ADHD--you're just special and different. But my ADHD is an illness that requires treatment. A lot of people will tell you that the only reason ADHDers struggle is because society is set up wrong, but I don't think that's true, at least for me. Being unable to remember anything, unable to self-start, and hypersensitive to rejection would be massive problems in any world. Sure, the world today is particularly brutal for ADHDers in a way we could probably mitigate if we reorganized society to be kinder, but that doesn't mean ADHD isn't ultimately a disorder that some people need to treat with medication and therapy.
I suppose that's fair.
full disclosure, im still trying to figure it out after recently revealted to that having ocd counts as neurodivergency.
I'd say just about anything that is typically referred to as mental illness counts as neurodivergence. But I'm not an expert on the term or its usage.
The difference definitely is in the nature of HOW divergent the brain structure is, how long it has existed for (since birth?) and if it could be altered for good to the point where it may be considered socially typical. Seems like there is no cure for OCD, just personal treatments.