I would assume that the Amish don't get their autistic kids diagnosed because they don't take them to (regular) doctors.
Besides, a lot of "autism" diagnoses these days are just slightly quirky middle class people with social anxiety looking for a label to explain their unease. Really heavy and obvious cases of autism are rare, such that it's plausible that you'd have zero reported cases in a small community or town.
Studies into potential links between vaccines and autism aren't only done by the pharma industry. They're also conducted by national/public health and research institutions and universities.
Given the decades of intensive research that's gone into this at this point, it's unreasonable to think that there's an enormous international coverup that virtually every government in the world partakes in, with not a single whistleblower coming out to expose it. IMO it's approaching Illuminati levels of conspiracy myth in terms of absurdity.
