Thinking of autism in severity terms is simplistic. In the UK we don't generally describe autism level precisely because an autistic person's "functionality" is a lot more complex than being inherent.
For example, for the sake of argument two people are born identically autistic in terms of intellect, genes etc. One is born into a family of people who know very little about autism, who are loud and chaotic, enjoy spontaneous days out and treat the autistic person's distress as bad or wilful behaviour. The other is born into neurodivergent family who are quiet and bookish, who prefer to plan ahead and be fully prepared for days out and holidays, who have a good understanding of autism and go out of their way to accommodate the young person and adjust their expectations. Despite their "autism" theoretically being identical, their experiences, degrees of difficulty in their context etc are going to vary wildly. That's because autism HAS to be considered in context.
I guess it also depends on your definition of what is severe and what is mild. I think a pp tried to touch on that by saying if your child is "severely" autistic and nonverbal they are more likely to get their needs met. I think that was rather clumsily phrased but I think what the PP was trying to express is that distress and overwhelm happen when you, your environment, and the expectations on you are too far apart. This can happen to a preverbal autistic young person with intellectual disabilities in a care home, or it can happen to a highly intelligent young person at Oxford university. Who are we to decide that one autistic person's distress from the mismatch between their neurology and environment are "less bad" for the person at Oxford just because they are verbal and academic? When sadly it has not been especially uncommon that the distress has got so significant that autistic people have taken their own lives?
My own autistic adult child was a very happy and functional quirky child in a family where they were well understood, and would have been "level 1" autism in terms of functioning labels up to about age 11 or 12. When expectations in terms of workload, stress, puberty, the social and sensory environment began to outstrip their coping skills they began to struggle and need more support. At 17 they had a full on breakdown and spent 5 years in a darkened bedroom barely getting dressed more than once a week and being forced to wash once a fortnight. It was only when ALL expectations were greatly reduced except what they enjoyed and special interests that we began to make any progress. Now at 25 my DC can get a familiar bus home from a local group once a week, gets dressed most days, cleans their teeth, washes once a week on their own, puts their washing in the linen basket and their plates in the dishwasher, but is a lot less independent than my 14 year old. This is not "mild" autism. They are unable to work but this year we are hoping to begin two hours a week volunteering.
It depends on whether you think autism is mild if it doesn't enormously affect other people. Some autistic people have predictable needs (which doesn't mean they are easy to support and certainly very hard to manage as a parent) and others have needs which may fluctuate. To me severity or mildness of autism doesn't really work as a concept because it's context depend as well as person dependent, fluctuating or permanent, internalised or externalised.
So in a nutshell, yes I would be cross if my young person's autism was described as mild because it has certainly massively impacted them, even though they are verbal, intellectually able, knowledgeable, and not difficult to manage behaviourally.