We have similar in our family. Without Covid, DS would never have been assessed and his ADHD identified. DH would never have gone 'OMG that explains my entire life' and been assessed and his ADHD identified. I wouldn't have gone into autistic burnout (which I still slip back into at a touch of a button so not sure I'm actually out of it) at the same point that we have ND on our heads and actually understand how the assessment world works, and so would probably never have been assessed for autism (or not for years more), and I certainly wouldn't have been assessed for ADHD. My daughter's assessment was at her request because of my son's diagnosis, and also I had the confidence to believe I wasn't a complete idiot to have her assessed for autism because I had been diagnosed. Covid actually triggered everything. I may have eventually gotten there on the autism diagnosis but the ADHD for my son and husband would probably never have been diagnosed and meds are making a material difference to their lives.
On the 'buying a diagnosis' point - I have no doubt that there are medical professionals/clinics that exist that you can just pay and they'll give you any diagnosis you want. Of course there are. Thing is this isn't an autism/ND thing - this exists for any medical diagnosis. Pay enough money and you'll find someone willing to take the risk of being struck off and will give you a cancer diagnosis, or say you've broken your leg. You'll find bank workers willing to confirm a much higher salary and solicitors willing to fake an asset sale. There are always unethical people who can be bought. It is a tiny proportion of diagnosis and honestly the people who can afford to pay for this are rarely aligned with the people who would have any interest in purchasing fake autism diagnosis for their child. What is far more common is non-professionals not really understanding what leads to a diagnosis, not having the full background of a case and (for attachment disorder in particular) not appreciating that a lot (non-profound) autism is genetic and it is quite possible to have a child who is autistic and have been (objectively) a shit parent because your own challenges with autism mean that you have struggled to parent well. A child being autistic doesn't mean they've been parented well, and it doesn't mean that better parenting couldn't improve the situation.
I agree btw that there is some uncertainty over the diagnostic criteria for autism and considerable discretion left to professionals in how to determine whether those criteria are met. Again I disagree that this is an autism specific thing or this does actually mean that autism is being over diagnosed. A lot of medical diagnosis is an art not a science. And there will always be situations where one professional says no, and one says yes. Again, I would need a lot more evidence than I have seen to persuade me that the difference means over diagnosis not under diagnosis, particularly for girls/women.
I'll go back to my own example. I ended up with the most expensive clinic in my town. That was because they had a reputation of doing a very thorough review, and also a reputation for having the experience to identify autism in masking women and girls. I wouldn't be surprised if they have a higher rate of diagnosis than average for the town because they're better at diagnosing (an alternative psychiatrist I spoke to asked in my initial discussion with her whether I had started talking late, like this was anything to do with anything!).
I don't agree that's because you can flash the cash and get a diagnosis. This is because (a) I clearly instructed them for all assessments that I was not interested in a diagnosis unless they were confident in it aka I wasn't hoping for autism, in fact the opposite, (b) for DD I mentioned (probably obsessively) that I wasn't sure, and I didn't know what NT looked like, and that I thought she was probably an edge case but not autistic, and (c) for DS I said that given they'd diagnosed DD as autistic, I was 90% sure DS was (but also that he didn't want to be autistic and that I would love it is he wasn't). If the diagnosis was in anyway influenced by what I 'wanted' then it would have come back with DS autistic and DD NT. It was the opposite.
I just do not believe that autism is (a) materially overdiagnosed (although I accept that there may be a question on whether the diagnosis is now too broad - DD and I would both be Aspie in the old world), or (b) a diagnosis that can be obtained by a parent knowing what to say, or coaching their child on how to act. DD is acknowledged as one of the best actors her drama teachers have ever seen [stealth boast], even she couldn't hold up her mask effectively enough for the assessors. I don't believe another child would be able to hold up a mask pretending they were autistic for a whole assessment. If you react in an NT way to social cues, then you do that automatically.
It really frustrates me that people, including people with autistic children, keep harping on as if there's this whole raft of people who are misdiagnosed out there. It's a dangerous narrative but it's just not true - yes there are some who are complete fraudsters (there are also people who fake cancer), and yes there are mistakes and you make get some children diagnosed with autism who have another underlying issue. The narrative that this is particularly an issue for autism, and that parents are buying diagnosis is just bullshit.
I do think there is a whole raft of parents who have not yet/are not planning to go through assessment for their child who believe their child is autistic and are wrong because it's some other condition or bad parenting, or both. People really don't know what the condition actually is. I have a family member with an autistic boyfriend who is absolutely shocked DS isn't autistic because he's so like her boyfriend, and that's someone with a degree of familiarity with the condition. I thought DS was autistic, and I am autistic! I think this can be a problem because there's a group of these parents who don't qualify statements when they say their child is autistic (not 'he's on the assessment pathway', or 'we suspect' but 'he is') and this makes people think that diagnosis is far more common than it is. BUT this isn't people buying diagnoses, it's a result of long wait lists, the trend towards deciding that self-identification for anything is ok, and the fact that if you have a child with additional needs you have to fight so hard for them, there isn't room to allow anyone to question whether they do have those needs.
I'm not sure what I think of the self-diagnosed adult autistic influencers. On one hand, I've never personally met an adult who's been certain, pursued diagnosis and hasn't been diagnosed but on the other hand I tend to hang out with middle aged female autistic women managing boring office jobs and kids, rather than influencers, so I may be self-selecting. In my (adult) world no one gets any advantage from saying they're autistic when they're not - in fact the vast majority of people hide it. I am a bit wary about someone willing to take on such a role of explaining what autism is to the wider world, who hasn't actually had anyone independent confirm it.