This makes tulpamancy sound like a voluntary version of what happens when multiple personalities form due to childhood trauma, but that wasn't how the original article made it sound.
From what I understand, recognizing each of the personalities and integrating them into a cooperative "system" is the standard of care for multiple personalities, but trying to induce this voluntarily is a lot different from just creating an imaginary friend.
In this case, a tulpa would share, and sometimes control, your own body.
There is some controversy regarding multiple personality disorded. From what I remember, the amount of multiple personality disorders diagnoses exploded in the 70s and 80s in the USA while the same disorder is rare in the rest of the world.
If people are able to generate Tulpas, it might mean that these multiple personality disorders were in fact generated by the psychiatrists treating these people. This could explain why there was such an increase in the USA while at the same time do not require large number of patients lying about what they are experiencing.
From what I understand, recognizing each of the personalities and integrating them into a cooperative "system" is the standard of care for multiple personalities, but trying to induce this voluntarily is a lot different from just creating an imaginary friend.
In this case, a tulpa would share, and sometimes control, your own body.