The severity of autism cannot be quantified easily. Some autistic people who communicate using words are considered to have mild autism whereas those with non-verbal autism are seen to be severe.
I have meet very intelligent and eloquent autistic people who are severely debilitated by anxiety and problems with independent living. In contrast, I’ve met people with learning disabilities who have an enviable life because they are well cared for by people who understand and appreciate their differences.
How severely someone is affected by autism can vary depending on where they are, who they are with and what demands are placed on them.
So if we should want to quantify severity of autism; the person living it should be the judge of how severe they think it is, not professionals, teachers or commissioners.