Incorrect. There is no single cure for personality disorders, but that doesn't mean they can't be cured. Any mental illness that is not genetic and which develops due to external causes can be cured. There are many personality disorders, of which NPD is one. While there is no single cure for NPD, in fact NPD can be cured in many cases in one of two ways. Some can be cured relatively quickly with an antidepressant, which eliminates the symptoms, but most with NPD can either mitigate the disorder or completely cure it though talk therapy generally in under two years. It's absolutely true that one can learn to stop being an asshole.
Psychedelics could be an interesting line of study for personality disorder treatment as well.
But most importantly, we don't know, so making broad, absolutist claims is a waste of time.
I presume this is because the classification of these disorders is way to broad and unspecific as opposed to hard science diagnostics.
> (…) through talk therapy generally under two years
Would you have a good source for that e.g. a meta study?
> I haven't heard he is violent nor of reports of him berating and belittling others
I haven't heard about violence, but berating and belittling others seems common for him - it's practically his brand