No security cable, bracket, or whatever prevents theft. Anyone who believes that they do is deluding themselves. All they are is a deterrent. Okay lock systems will just deter the opportunistic thief; better lock systems will deter the more determined thief. But either way, with the right tools and enough time, any security mechanism will be able to be bypassed.
Strictly speaking isn't that still prevention, albeit limited? If I don't have a tool to cut through it I'm prevented from stealing it right now. Yeah, I could come back with cutters, and it wouldn't prevent me then, but it did prevent me the first time.