The problem with severity is that autism affects so many different things, not all easily measured, that you can't just give someone a unified functioning level. Also for many, those things change day to day, hour to hour. As well, we don't even know what autism is. There's an idea out there even supported by some research that people with a little autism may do worse than those with a lot of it. But then since we don't know how to measure a little or a lot... yeah.
Also the problem with assuming intelligence (whatever that is) will help a person overcome it, is that... the various cognitive skills that get called intelligence can't always do anything to overcome some kinds of sensory issues, social naïveté, cognitive blind spots, social confusion, etc. That works for some but not for all. I know a lot of very conventionally intelligent people who were labeled with severe/profound intellectual disability most of their lives because they couldn't and still can't overcome extreme sensory and movement problems. Many of them are far smarter(in the way that word is generally used) than I am, and I was labeled extremely gifted back when they were labeled profoundly intellectually disabled (and I'm no longer considered "gifted" at all). Not that I support conventional definitions but most people do. And I know many autistic people who despite current labels of giftedness, are always falling for the latest hucksters because of extreme naïveté, or are trapped in their houses from agoraphobia or severe overload. Cognitive or academic skills only go so far.
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"In my world it's a place of patterns and feel. In my world it's a haven for what is real. It's my world, nobody can steal it, but people like me, we live in the shadows." -Donna Williams