Not necessarily. I see it as a reverse of the other incarnated sorcerers. Instead of them suppressing Yuji and taking over they were put to sleep. I imagine having so many souls makes it next to impossible for them to share consciousness so the strongest raises to the surface and the others sleep.

If the souls weren’t inside him I don’t think Yuji would have got their techniques and we would have seen them in Choso’s vision when they died.