I don't know about these precise numbers, but ~57% of autistic people have an <85 IQ (cf. 16% in general population), and somewhere between 25% to 50% are nonverbal. So 90% may be too high, but it seems very likely that a solid majority has profound difficulties in life.
Note that these numbers are for autism diagnoses, not autism cases. Someone with profound difficulties in life is far more likely to wind up with an autism diagnosis than higher-functioning autistics that are more likely to figure out successful adaptations.
edit: my source is the CDC(https://www.cdc.gov/ncbddd/autism/data.html) for IQ and this paper https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3727194/ for proportion of nonverbal autism.