In the Catalyst Control Center, try switching the D:OS executable to integrated graphics. If the performance drops (or the game just crashes trying to load), the 0% load on the discrete graphics could be a bug in GPU-Z. If the performance is the same, switch the setting back to high performance and see if that helps.
You could also try setting it to automatic, and see if the game picks the discrete graphics then, even though it doesn't appear to when it is specifically told to.
