As an adult DAS guest, I just wanted to contribute a few thoughts to this conversation.
Many autistic adults are not formally diagnosed - particularly those of us who grew up when autism was less understood. Autism evaluation as an adult is very costly and usually out of pocket. It is in this sense a privilege to have a formal diagnosis. For autistic individuals in the UK, they can receive diagnosis through their health system, but the process can literally take years.
Furthermore, some may not pursue formal diagnosis even if they can afford it, due to the real stigma against autistic people. There are many who wouldn't want to come out as openly autistic. I understand this choice.
Lastly, what I need accommodation for is not autism per se, but my sensory differences. It is not uncommon for autistic people to be noise sensitive or just overall have a lower sensory threshold. (It is not just neurodivergent people who have sensory differences, there are certain medical conditions as well.) These kind of neurological differences are not usually diagnosed by a doctor. I do not have a doctor's note that says I have hyperacusis (noise sensitivity.) And IBCCES, who does Universal's system, will not give you accommodations without some kind of doctor's note.
DAS works like the old-fashioned, original Fastpass. We receive a return time. I have never used the maximum number of guests, but I believe the max is 6. We are not cutting any lines. We are asking to queue like everyone else, but in an alternate location that doesn't cause physical pain.
Edit to add, here is a page following the mentioned litigation.
https://www.pacermonitor.com/public/case/51814816/IL_v_Six_Flags_Entertainment_Corp_et_al