Indeed while you would like to minimize body pitch and roll as caused by forces like acceleration and going through corners it actually is important also for a car to be able to quickly follow the angle of the road. That is also one of the reasons most supercars have their engine in the center. Centering the majority of the mass at the center of the car will make it turn, roll and pitch easily!
However there is another reason why you do not want the gyroscopic effect. To store enough energy in a flywheel that doesn't weight very much requires extremely high rotational speeds which means the gyroscopic effects will be very strong. Strong enough to put a high strain on the chassis and destroy the bearings of the flywheel in the process.
I actually expect they are using counter rotating flywheels with a vertical axis. Suspended in a construction allowing (limited) free rotation on the other axis's and an electrical system to transfer the energy.