That is what spectrum means, and some autistic people say the word is not applicable to the concept of autism.

Yes, that’s true from the dictionary and the article is one place where its use makes sense. However, usually people say “on the spectrum“ to mean someone is a high functioning autistic. That is something that isn’t a helpful definition.

This has always driven me nuts. We're ALL "on the spectrum," if you just stop and think for a moment before saying it. That's what a spectrum is.

If you tried to quantify different people's experience of autism you could maybe compare people by the amplitude of their symptoms (say a maximum or average), but you'd get a much better idea of the range of experiences with something like a Fourier transform. Imagine different symptoms are different wavelengths of light. Different people experience certain elements of the constellation of symptoms that we can "autism" to different degrees. And the goal is not really to get anyone to be "less autistic", but to help them live in society (or to build a society that allows them to better join in).

The medical use of the word "spectrum" doesn't always describe a continuum, but classification criteria along multiple dimensions. Autism is no longer considered a "position on a scale".