"I do think the argument has become diverted between experts arguing what 'model' should be implemented - direct or indirect - without thinking of the actual work which will be done (or not done) with the child and how whether it will actually make a difference."
I think this is the key issue. I have been reading your threads for months and have to say I was not exactly clear what you were asking for and why
. I think you have to believe in the intervention you are gong to tribunal for, even if that means you are not entirely in agreement with your witness! If the NHS SALT can't do it then there is little point arguing she should.
I think it makes much more sense from this perspective - what your DS needs and why / what difference that will make to him and then let the professionals / panel try and put that into some form of intervention. It does not actually matter if its delivered by a TA, a social worker, an ABA tutor or a SALT what matters is the person designing the programmes and next steps knows about HFA / language / social skills and how to teach them. If the person setting and monitoring the programme knows this, then it can be delivered day to day by others (as an ABA programme is). I agree with Star your top 5 points, make them relevant to outcomes and specific egs of things your DS struggles with and how high quality intervention / coaching with these skills now will save money later on.
The advice I was given by someone who sits on tribunals (hope you get him he is lovely) is to keep it relevant and practical to the child. You are in danger of making it too technical and about policy etc - I think you are spot on with keeping it relevant to your DS.
It may be your argument is not just private SALT -v NHS SALT or direct -v- indirect. But actually that so far you have no-one on DS 'team' NHS SALT / outreach / school etc who has the expertise to teach the skills your DS needs, or to set the systematic programmes necessary and to monitor and evaluate them. You have found a private SALT who can. It seems to me it could just as easily be an ABA tutor or another professional eg specialist teacher who is experienced with HFA. So really its not about whether NHS SALT can deliver the intervention but that between them SALT, outreach and school do not have this expertise and therefore they have to go into the private sector to get it or 'buy in' significant EP or specialist teacher time.
In my area SALT would argue anything which is social communication or behaviour rather than pure language need is not their remit anyway but autism outreach's.
I think there might be some merit in arguing that this is what you have identified as missing from your DS intervention (give list and egs). Your solution has been to find a SALT with ASD experience who is able to fill that gap (and egs of successes). But there may be other ways of filling the gap in expertise but they are unlikely to be any cheaper than your solution eg private SALT to train up, monitor and supervise TA (I know the current TA is an issue).
I really think you have to be fighting for an outcome you actually have confidence will work.