About the plot of "Inquisitor: Martyr" (game)

So, i am playing the Inquisitor: Martyr game and the plot is about uncovering experiments made by the Mechanicus to use willing subjects, to turn them into demonhosts, purge the demon and the end goal is to have warp resistant, loyal former demonhost warriors.

Isn't that what the Exorcist space marines are already? If so what's the point of those experiments, we already know it works and how to do it with an acceptable degree of success