Re: the second part—in my experience, FWIW, people tend to assume a lot of autistic self-advocates are more high functioning than they actually are. Like, I think there’s a jump to assume that everyone who can communicate is the Aspie “quirky” stereotype but a lot of these people have pretty significant sensory issues, restrictive-repetitive behavior, etc, issues and would probably be seen as at least moderately severely autistic if you saw them in clinic. Of course, that doesn’t capture people at the furthest end of the severity spectrum, and I don’t know if there’s a good way to. Of course, you have parent/caregiver report, which can help, but that’s still a proxy report with all the limitations inherent in that, and, let’s be real, parents of disabled children don’t always have their kids’ best interests at heart (they often do, but the subset that don’t often really, really don’t).
I actually think this is a cross-disability issue—that less severely disabled people tend to have louder voices in the dialogue, especially if they are white, from wealthy families, and conventionally attractive, and their perspectives get listened to more, even if they aren’t necessarily representative. It’s one of the reasons that some of my colleagues who do a lot of developmental disability-focused work deliberately go out of their way to include more severely autistic people, people with ID, disabled BIPOC, etc, on their research teams, even though it often creates more work for them in terms of accommodations, pay, hiring, etc.