I think you have interpreted that wrong. They had to go to such an extreme set-up to get the front to turn in that there was no rear stability at all. Like a see-saw with the fulcrum too close to the front of the car.
There was already inherent rear instability in the F14-T to begin with, which was made worse with the extreme set ups Kimi needed. With a stable rear to begin with Kimi wouldn't have needed to go to those extremes.