While the graph is not made on any actual dirrctly linked data set I would still say it has more meat to it than just being nice. It's very much over simplified especially the "improved diagnostic and understanding" part.

That metric alone is at odds with its self in that our understanding of neurodivergence vastly out paces diagnostics. When most hear the term diagnosics they think of fancy medical devices that give either a yes or no answer which is completely the opposite of what is actually done. There is essentially a book with a set of "symptoms" that a group of doctors have agreed upon that ones doctor uses to comapre their patient to. While that sounds fine its far from flawless.

• The list of acknowledged symptoms is only updated every X amount of years (iirc its like 5 years but I'm on my phone so hard to check)
• Many of major issues/symptoms people face are completely mental therefore invisible with no way to test for them (atm)
• Much of the "testing" can be very opinion based even if it's based on something objective therefore finding a doctor who is the least bias.

(i could go on but need to stop procrstinating)

All of this doesn't even touch on thr social or economic aspects too.

Back even just 26 years being diagnosed with ASD, ADD, or, ADHD came with heavy stigmas with many parents refusing to get kids tested because if it was "positive that means there's something wrong with my kid"

Also there could be a huge drop in current diagosis due to political persicution.

Depending on where you are it can be cost inhibitive.