So far as I am aware, the only thing the dream-sleeve does to souls is strip them of identity, and then store them for later use. These souls, even when stripped, are still connected to the original spirits - the et'Ada - Aedra. Though, I guess this has more to do with opinion than either being pure fact. I enjoy the idea that mortals are the lesser forms of the spirits that made them. If you have solid proof that it's not so, then I'll of course change my views.
If you're operating on this assumption, then this might explain your thinking.
That's not quite what happens. When a soul goes to the dreamsleave, the soul is added tot he collective of souls, mixed together with the others, and a new soul is carved out using pieces of the others, hence the collective Hindu-esque nature of the Mundus.
Read up on http://www.imperial-library.info/mwbooks/lessons.shtml, http://www.imperial-library.info/obscure_text/vehk_teaching.shtml, http://www.imperial-library.info/obscure_text/nu-hatta_nu-mantia.shtml and http://www.imperial-library.info/obbooks/mythic_dawn_commentaries.shtml.