I can possibly answer #2.
I was diagnosed with autism in my early 40s. I've also now been referred for an ADHD assessment. I'm in my 50s.
Your most recent post shows a fundamental lack of understanding for a start but I'm going to ignore that for now.
When I was a child, I was the 'weird kid'. I didn't really have many friends. I just found people very difficult to understand. And they clearly didn't understand me either. I had very specific interests that no one else shared so it was hard to find common ground. I wasn't naughty but I was a misfit. I didn't really know that at the time though.
I've been a teacher for 20+ years. I've never disclosed it at work (due to potential for prejudice). So i don't have any 'offical' reasonable adjustments but I know what my limits are so I work according to my needs and I'm transparent about these and negotiate deadlines (for example) where necesary and appropriate. There is no slack for anyone else to pick up and no one else does any of my work. They can't. No one is negatively impacted by it and it's never been a 'problem' or raised as one.
My adult children are both diagnosed with ADHD (one also has dyspraxia and the other is also deaf).
My eldest graduated and works full time and has learnt to work within/around their needs, is progressing well and earns well for their age. My youngest is at university and will be entering a regulated profession and already knows what their 'accommodations' will need to be and that it is their responsibility to fulfill statutory obligations regardless of their own needs.
So you ask where have the naughty childen gone? As understanding has increased, some of those 'naughty children' are recognised as having been undiagnosed. ND presents differently in different people. My own issues have been present my whole life but I flew under the radar because girls have been undiagnosed for years becaue autism presents differently in girls to boys and the diagnostic model was based on boys. So girls simply weren't diagnosed in the past. They still had autism though.
Eg generally, girls are better at masking and copying social norms. Girls are also more accepting (through socialisation) so are more likely to overlook another girl's odd ways than boys are (due to their socialisation).
Education is very different now to it was when we were at school. It's far more rigid, the curriculum is packed, there is more to do in less time and many children struggle with numerous transitions, cognitive overload and lack of opportunity to consolidate learning (and not just ND children). Those children would have coped (as I did) with the school experience I had but are unable to cope now so are more likely to be flagged up and diagnosed.
I have three nephews. One has complex learning and physical disabilities but all are diagnosed with autism and have been since early childhood. All attended special schools. One has a degree and a masters, one is currently at university and one will never live independently.
I don't recognise the pattern of causing unhappiness and difficulties in family dynamics because we are an ND family so we don't work to NT standard rules and familial expectations. We have no issues in our family, despite the level of need within it, because that's the way our family is organised. The Maori word for autism translates as 'in their own time and space' and thats largely how our family operates. Lower demand, lower stress and so, ultimately, everyone thrives.
From what i have observed, autistic people struggle the most when born into a largely NT family because, despite people with autism being labeled as 'rigid', there is just as much rigidity in NT people/expectations but they regard their rigid understanding and expectations as 'normal' and get frustrated when ND people's needs/ways don't match.