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.
That's a fair perspective. However, the counterpoint I've often heard from autistic advocates is that autism is only a disability on allistic terms. If everyone communicated in a way autistic people understood, it wouldn't be a disability. This could be completely wrong, of course, but it's what I've heard argued.
I don't feel like this is the case with my variety of ADHD. I feel like even if the world tried to accommodate my ADHD traits, I'd still struggle quite a bit.
While you do have a point that autism can be mitigated by society, in a way, so can ADHD. There isn't just one model of disability. There still is that disconnect from allistics that autistics have, and some autistic people do in fact go to therapy to help mitigate issues with their autism (note here because I feel it's important: a) autism is often comorbid with things like sleep disorders, OCD, depression, anxiety, etc and a lot of therapy for autistic people does revolve around that and b) I am absolutely not referring to ABA which is just conversion therapy).
Also, when I mentioned me being autistic and only using neurodivergent to mean the collective of disabilities mentioned previously, I had also meant that it felt like to me that you were proscribing a meaning and/or an impact of the use of the term neurodivergent (and neurodivergence by proxy) that did not exist, one seated in prescriptivism. I don't particularly see any negative impact to people using the term(s) either online or in real life and I've seen multiple people who are neurodivergent themselves use the term(s) to refer to the collective community of disabled people as just a label. While I can just offer up the "It's just a label that we're using to mean [insert thing here]," you could argue that I can't do that because of the impact, but I have not seen such impact. I and some others on here have compared the term(s) to the word "queer" used for people in the LGBTQ+ community, although it has a trouble history as a slur but the community is reclaiming it and using it for their own despite its problematic past. But unlike the "queer" label (used to mean identities falling under the LGBTQ+ umbrella), the "neurodivergent" label (used to mean the collective of disabilities) doesn't really have such a past. Nor does it have such an impact either.
Because I'm itching to, I'll go further with that queer-neurodivergent comparison. Not only is "queer" used as a catch-all for the LGBTQ+ community, it's also a label itself used to refer to someone who doesn't want to label themselves specifically but rather is just not-straight. Neurodivergent can be used in this way as well referring to some kind of disability along that spectrum but not necessarily identifying it in any way. Perhaps one doesn't need to identify their disability because they know the symptoms and they have coping mechanisms to help them mitigate those symptoms. Perhaps they don't have the resources to go narrow down that label into a more specific one. Or perhaps they don't care.
Really, as a TL;DR to this comment, the label isn't doing any harm and, at least in my perspective, does nothing to belittle or minimize the struggles of the people in the ND community.