I also saw little Blaine as a part that had segmented itself from the crazy Big Blaine part, like the tiny sane part of a brain that may metaphorically brick itself into a safe niche from the insanity raging through the rest of the brain.
Yeah. Blaine was crazy from being super intelligent and having nothing to do for centuries...but I don't think he had a dissociative identity disorder. Little Blaine was more Blaine than Detta was Odetta. It was a voice in his head, not another personality entirely, and it manifested itself as a separate part of the same entity. Just like how he used a lot of different voices to talk.