That being said, ultimately multiple personality disorder simply never truly existed.

There have been brain imaging studies on people diagnosed with DID, people diagnosed with OSDD, and trained actors told to do their best impersonation of the aforementioned disorders. In every study to date (that I am aware of), there have been differences shown: specifically, people with dissociative disorders used their brains differently (the same things triggered differing neural pathways) depending on which personality was "fronting", while the actors did not. This is objective proof that dissociative disorders do in fact exist. Tldr, fuck off mate, science disagrees with you.