It isn’t uncommon, I’m afraid. The majority of parents who appeal are successful.
Is your preferred placement wholly independent?
As well as the evidence from the CAT team, EP and ASD diagnostic assessment, do you have other evidence? For example, OT and SALT.
When you received the draft, did you propose all the amendments that are required and reference the evidence?
I would go back over the reports because LA EP reports are often not brilliant and sometimes people don’t realise that until they dig deeper. For example, look for wording such as “access to”, “would benefit from”, “regular”, “up to”, “or equivalent”, “opportunities for”, “as appropriate”, “would be useful/helpful”, “such as”, “e.g.”, “etc.”, “as required”, “as advised”, “key adult(s)”, “small”, “small group”.
I would also remind they should have finalised by now.
Not commenting on your case specifically, but the LA is right that a child not managing mainstream without an EHCP doesn’t automatically mean mainstream with an EHCP isn’t suitable.
Is alternative provision in place?