9% is nothing to be honest.
The simulated feathered torque is 10% so in an engine failure the plane can have 90% torque split between the engines.
At 9% imbalance they will be well away from V minimum control airborne issues, Vmca.
The roll is just a secondary effect of yaw which was obviously not controlled. And to be honest with the experience level of the FO I can understand the reasons why as well.