I agree, the terminology is confusing. It is extra confusing because the intent is to capture both:

1. Different autistic people may vary in which symptoms are most severe while all still being autistic.

2. Different autistic people may vary in the overall severity of all symptoms and how much it impacts their quality of life. (At the same time, there is still a distinct cut off where you are not considered to have autism if it doesn't manifest significantly in your life.)

The latter point is why "Asperger's" is now simply lumped in with ASD. But that tends to obscure the former point which is also important.

Perhaps "cluster" would have been better, but here we are.