> because our diagnostic threshold for tallness has lowered?

The threshold for being diagnosed as autistic has increased in recent years. As Asperger is not a separate diagnosis anymore but is part of ASD, some people that might have gotten an Asperger diagnosis would not get an ASD diagnosis today.

Again, a diagnosis requires that you have care needs. If you don't, you will not be diagnosed. There is no slippery slope of lowering standards.

There have always been neurodivergent people. Not long ago, here in Germany autistic children were systematically murdered during the Nazi regime.

The difference is that neurodivergent people don't have to hide anymore as much. We finally have at least a bit of a voice.