Stillloving, will try to address your points.
I get that the therapists have extensive experience, I would never in a million years suggest that in general I knew better than they do about all children. Like I said, their very brief advice for dd (anxious but straightforward, no masking at all and is happy to talk to anyone) was spot on, we followed it and five months on we can honestly say that things have turned around for her.
For ds2 though, he is complex, but in an appointment situation he looks like any other child, he looks straightforward. If I had £1 for every time people have met him and assured me he's fine when he's not, I'd probably be able to afford a holiday!
I know they have a genuine wish to help, but when they see a normal child, looking happy and relaxed, appearing to engage fine, it is so at odds with what Dh and I have told them that they can't get their heads around it, no-one can. I believe this is what makes them think we are liars, before we had Ds, dh and I would probably have the same opinion!
So they want to help this child, and in order to do that, they need to sort out these dreadful parents who are telling them awful things about this child who is clearly fine. How will they do that? Encourage us to treat him like the normal child he is, encourage us to shift our relationship methods with him to stop us from seeing him as a "problem" child when he is obviously (to them) not.
I can see exactly why this is happening, and I'm certain they have our best interests at heart, but when their view of us is so much at odds with our reality, and they won't believe what Dh and I have told them, it puts us in a worrying situation, worrying for Ds (as he can't access support) and worrying for us (as we are wide open for accusations of all sorts).
We have filmed and voice recorded evidence, but they won't look at it or listen. I've taken in a folder full of notes Ds has written about wishing he was dead, drawings of him dead, drawings of him killing himself, but it's all dismissed as silly boy nonsense. Notes by the way that had my hard-as-nails neighbour in tears.
I entered into our "relationship" with CAMHS fully trusting them, knowing that we were in safe hands, relieved that our worries were at last being taken seriously, and ended up so disappointed and scared by the whole experience.
Had I seen them only for dd, I would be here saying that CAMHS were wonderful, but for ds2 they've believed the version of the boy they can see, even when it has been explained over and over again how well he masks.
I also find the suggestion that a dx is only an opinion worrying. A diagnosis of autism is not easy to come by, not something that any team of diagnosing professionals takes lightly. Suggesting it is only an opinion says to me that it is common for a diagnosis to be ignored (please tell me this isn't the case!). Our son's diagnosis has been utterly ignored, so perhaps it is the normal CAMHS view? Which is gutting, as we naively felt that his dx meant we no longer had to prove his difficulties.
I have completely lost my trust in CAMHS following their involvement for ds2.
Over the last few years, we have had to be very open minded to work out what was going on with ds2, how to help him etc. It always seems to be the case that we have to be open minded about accepting others' views, even though we know, from extensive experience and beyond shadow of a doubt, that we now know what is going on and how best to handle things day to day.
Why is no-one ever open minded enough to take in what we (and others like us) are desperately trying to say? Why are we, the people who live with our children, always wrong and have to have our experiences dismissed in favour of people who don't know him?
And if I sound defensive, too right I do! How would you feel knowing something as fact and it being twisted and turned into something else and being powerless to do anything about it? (parallels with gaslighting?). It seems the only way we can prove anything (in school and for CAMHS) is to stop using the strategies (that keep Ds calmer and us sane ) and allow him to spiral into a breakdown (or at worst a suicide attempt) so others can see it, but we're good parents, we will do everything in our power to keep Ds safe and progressing.