Thats a cute observation but real facts are the following:

• Autism was only formally recognized in the 1940s - there’s no reliable data before that, though historical evidence suggests autistic people have always existed. For decades, people deemed “mentally ill” were institutionalized and hidden from society.

• The majority of autistic people can mask their traits and present as neurotypical - they had strong incentives to do so given the historical stigma.

• Diagnosis happens more frequently in areas with accessible healthcare, which naturally are also areas with higher vaccination rates.

• We now have better diagnostic tools and a less punitive society for people with neurological differences. The diagnostic criteria have expanded significantly - many people (especially women) who wouldn’t have qualified under older definitions now do.

And if we want to include the more modern research done by the autistic community we learn that autism is a part of a bigger phenomenon called neurodivergence which includes adhd and many others. Who also used to be completely excluded by the dogmatic labeling of neurotypicals.

Also you referring to autism as a serious disease shows how little you actually know about it. Just like anyone else neurodivergent people can have psychological disabilities but because they are neurodivergent those disabilities are often different from neurotypical ones. In ““high functioning”” autism disabilities are subjective in context of living in a neurotypical world and are increasingly less disabling with social acceptance and understanding.