A diagnosis opens the door to access services like occupational therapy, speech and language therapy (which includes feeding therapy), physiotherapy, psychological support, and educational intervention , which are offered according to the needs of the individual. It’s not like there’s an autism package that’s one size fits all.
On top of that it’s recognised that autism usually presents with comorbidities, and referrals would be made to other medical specialisms, as and when.
The decisions about what to work on are made through a combination of standardised assessments, professional judgement, parent’s concerns and priorities and referrals.
So a child who has been misdiagnosed with autism, may be accessing the services and support that they need. There is quite a range of relatively rare but similar-ish syndromes and it makes more sense to invest more funding in post diagnostic services than splitting hairs on the finer points of diagnosis. Not saying that’s ideal but it’s pragmatic.
I haven’t met anyone in the parent support groups that can’t name multiple relatives across generations that share obvious traits so I cannot believe it’s produced by screens and chicken nuggets.