@freemo first of, let me thank you for giving my stupid take your very valuable time, I really appreciate it!
I think I, as always, missed main point of your post
> My concern is that even with a diagnosis I’d still remain convinced 95% of people diagnosed do not have it (and this comes from a lot of discussion with experts).
it reminds me a book? or a story? when guy was reading a medical book and found like hundred different illness and disorders in himself
people (especially youth) are very impressionable, so I like your choice to call it "designer disorder", since is 1) everywhere on social media, 2) fancy and 3) gives you social (victim) points, so a lot of so called people on the spectrum are just lucking social skills (yeah, irony, I think I have more of this than actual problem)
to add something valuable to conversation, I remember recently I was listening to a podcast (Peter Atia? Uberman? or Shane from Knowledge Project? one of these guys) when host had a guest, forgot his main specialization, but he told a story how he had a stroke, and after he found out, that we basically live in illusion, we as humans have multiple systems for reality check, but his stroke disrupted seamless work of them all as one "mind", that was unexpected perspective.. dunno.. to how fragile we are and how our brain does a lot of work to interpret reality
now I regret that I picked math instead of neuroscience, brains are much more interesting