I think everybody only 'knows what they know'.
For instance, I know that I have seen a documentary about a woman of low intelligence who has DID. She was extremely low functioning and needed a full time team of carers to assist her. Until then I also believed that one of the 'criteria' of DID was high intelligence... or at least, that is what my T had told me.
It would be nice to believe that DID requires a high level of intelligence and creativity (that would mean there has to be something 'right' with our lives, right?) but I don't think that is the case. However I do think that those dissociative people who have a high level of intelligence and creativity are perhaps able to 'use' their dissociation more effectively and may have a better outcome. Maybe a higher percentage of people with DID who have lower intelligence end up in jails (or worse). What I do know for certain is that there are people with DID who have below average intelligence.