My spouse had a therapist that tried very hard to convince them that they had MPD (before it was rolled into DID) and repressed memories; they dumped the counselor. And yeah, they have CPTSD from familial abuse.

The perspective I'm coming at this from is that a lot of these super-fringe ideas really got off the ground with the Satanic Panic that started very small in the late 70s, and went on through the 90s; you had groups like RAMCOA (Ritual Abuse, Mind Control and Organised Abuse Special Interest Group) that pushed really wacky ideas as being absolutely true, you had people insisting that repressed memories were 100% real rather than being things that you'd simply forgotten or fabricated memories (the work of Dr. Elizabeth Loftus shows how memories can be fabricated, and strongly suggests that 'repressed memories' don't exist in the way that was popularized in the 80s), that multiple personalities were 'fractured' personalities that sprang into being to protect the self, and so on. The people that came up with these batshit ideas are still around, pushing the same nonsense, but they keep changing the names to try and give them a veneer of reasonableness.

And yet, if that's the way that shit really worked, you should see that often with highly traumatized people; you should see DID and repressed memories in soldiers that have been in intense combat, in torture victims, in people that have lived through extreme, long-lasting abuse from parents and partners. Instead you see people that can't forget the terrible things that happened, people that have a trauma response with certain sounds, smells, etc. (triggers).

How about projection? As in, you imagine a personality/character and you project it upon yourself as to become said person. What would that fall under?