Experience of first autism assessment, felt like a benefit assessment.

A summary of what we think happened is below.

From the start the assessor was caught up on that I wasnt referred via adult social care, and was done via GP. He never really let this go through the entire hour.
Most of the assessment was him asking me why I think adult social care, my school, and my parents didnt raise the issue. (bear in mind as well I was at school in 80s and 90s).
There was no talk about symptoms from him, this only happened when me and my sister brought it up and he changed subject.
When my sister gave him some evidence she had, he told her if she cant provide evidence he cant take it into account. Then said "interesting" when she said she had no evidence to hand.
He initially told me I should be having a ADHD assessment, when I said I have Autistic symptoms, he said it sounds more like ADHD but wouldnt explain his reasoning.
Later on he moved to depression, when my sister asked him to explain what is leading him to that, and how it would explain my childhood behaviour he stopped engaging with her and asked her to leave.
After she left is when I was asked why I wanted an autism diagnosis.

Even if I have another assessment and it goes better, I dont want another person to go through this with him, which is why I think a personal complaint needs to go in. I have never been spoke to like this before.