"Powers" are born of awareness and Will. They are not super powers as is commonly conceived and viewed.
As was originally being explored in this post, a soul is far more complex than simply being an aspect of someone that can be taken away like an object, or trophy. It is the collective whole of that individual's identity.
It is easier to define in the terms of lesser spirits, because they very much set within specific roles and their entire identity is based within that role (generally speaking). Greater spirits (demons, angels, some fae, etc.) are so great as to have much broader identities, that can take a lifetime in some cases to fully grasp and understand.
Human beings, as well as most other living things, possess spirits much like these greater spirits, that are not wrapped up entirely within the one lifetime but expand far beyond this into what may be many lives, existences, or generally the greater whole of that spirit's existence. What's more, a living thing is constantly growing, facing new things, and changing, so the identity, Will, and so forth that creates the soul is forever evolving.
So then how do you take away someone's identity? How do you take away such a complex and layered and ever changing thing? And even if you do so, how do you keep it?
Things of this nature simply do not work like this.