It isn't surprising people don't like being defined by how others see them as lacking, whether it's mildly or profound.
Describing other people's disability as mild has a long history of being used to avoid giving or removing support and consideration. This can put people back up and bring concerns, particularly as that can and does lead to the disability getting worse without notice. It can put people's lives at risk.
Describing other people's disabilities as highly or profound has a sickening history of dehumanisation by those in power, which makes some wary to use that kind of language. It can put people's lives at risk.
I think just as the diagnostic criteria and naming for autism as changed over time, it will continue to change. I do think there could be benefits to clearer language, there have been a few frameworks put out there and some research attempts; however any framework we use will have limits - they largely rely on a deficit model to define, which amplifies problems and ignores how people change over time or in different environments. Moving beyond that, while a dream, is not something I see as realistic. Part of all disability work is discussing disability and people far beyond just the diagnostic criteria.
And then there is is the issue that once diagnosed as meeting the criteria for ASD, it can be difficult to get professionals on side or just not a priority with limited energy and time to get past that difficulty for other diagnoses or other non-medical causes of issues so everything deficit-wise can get put under that diagnosis. Autism is not unique in this, but it's a very visible example of it, to the point that there has been discussions around ASD masking other conditions that it is co-morbid with. I mean, until recently, people couldn't be diagnosed with both autism and ADHD, and some professionals have come out with concerns about the lack of resources and barriers to a FASD assessment even with data showing FASD to be as to twice as common as ASD, and that the overlap in symptoms and ASD being highly co-morbid with FASD may mean some are not getting the full care or understanding of themselves needed as ASD is more socially acceptable and 'easier' to diagnose as there are far fewer professionals available to assess and there is the need for parental history to confirm with FASD.
Their struggles are trashed because they don’t fit a picture of what others think severe autism should look like. It’s frankly disgusting. No other disability gets this.
I agree this rhetoric is very visible when it comes autism, or neurodiversity in general, especially in how it is discussed online, but people with other disabilities also deal with the issue that if it doesn't look like what other people think it should, then it gets trashed. Disability in general leads to that issue where people's struggles are trashed if we don't fit what others think disability looks like alongside being trashed for not fitting what others' think 'normal' looks like.