Both of the systems can be made to be on at the same time (or actually all three systems). The torque is not flat, it's flat in the beginning, then it reduces opposed to the rpms. So electric is better at low rpms while gasoline are better at high rpms. But as the electric motors drive the rear wheels and the petrol the front, it becomes a little strange, since the petrol has a gearbox, while the electric doesnt