I don't think it's particularly common. When I went through my dx, I was really hoping for adhd because then I could get meds, but my doc and all my screenings were like, "definitely not adhd, definitely autism".
So, maybe you are seeing rising diagnosis rates and considering that too easy? If encourage you to think about why you feel this way.
I had one good PDoc who helped me, with my genetics, not to diagnose me, but to help me find what helped me and my specific symptoms. Diagnosis is not as helpful as looking at your own symptoms and own history and using that to find what helps you.
It's not about the rising rates, that could be explained in other ways.
So then you grow up as autistic and/or ADHD person which creates a lot of social friction and conflict in your life, you're called lazy, careless, difficult, overly sensitive, and this is particularly bad if you're undiagnosed. You don't fit in socially so you develop social anxiety (this is par for the course), and after a while that can spiral into depression or even a personality disorder, you might start to self-medicate which can turn into a substance use disorder, and ultimately people afflicted by these disorders are taking their own lives at alarming rates. You should look up statistics for suicidal ideation among children and adults with autism for a reality check.
Most of this can be prevented if those affected were diagnosed and offered support as early in life as possible.
So no, having ADHD and autism, two very closely related neurodiversities, and then developing anxiety as a result of that is not at all unusual.
The diagnosis is a road to help. I doubt many people travel down that road without there being some merit to their ideas, but even if it is the case that lots of people travel down that road, that doesn't say great things either. That just means we have a giant group of people screaming out for help and they are using one of few outlets to try and get it. I'd rather they get that help through travelling down that road than blocking off the road to anyone isn't 'actually ill', whatever we define that as.
It’s something new that started happening to me in my early 30s. I can’t seem to get a diagnosis. Wondering if it’s autism related.
I’ve been to a bunch of specialists and they say it’s all in my head. But car headlights look 10x brighter than they should. And cutlery sounds 10x louder.