I often feel bombarded by people who praise early diagnosis of ASD. There are lots of benefits of receiving a diagnosis as a young child, for example being entitled to receive support at school. However, there are also some benefits of not getting diagnosed until adulthood. I think that I am a better person in many ways because I wasn't diagnosed with ASD until I was in my twenties.
The period of time in which a person is diagnosed, for example 2019 versus 1999, would also affect how useful a diagnosis was. For many older adults, having a diagnosis as a child would probably not have helped them much at all, just because of the period of time and the widespread lack of understanding of autism.