The TAR is not a transition world between the real world and the "soul pool" - only the Heroes of the Horn seem to exist there, waiting a chance to be re-spun. It seems to be a psychic plane that is inhabited by the residual mental energies of those currently living. As far as we know, souls return to the Wheel to be spun out at a later date, not to T'A'R.

And the fact that TAR and the Blight are separated does not prove anything either way - it is just as likely that the DO manipulated TAR to erect defenses protecting It's forces from direct attack, perhaps because it is in TAR that the DO is more vulnerable compared to the physical world.

My personal theory is that the bubbles of evil are caused by the Dark One's presence as well as exacerbated by It's growing influence (so in a way, it is a chicken and egg scenario).