Roll stiffness != cornering stiffness. But they do both have an impact on vehicle sideslip and/or understeer rates.
For example with cornering stiffness... for grins let's assume we have a bicycle model with 50kg F/50kg R static split. Heavy bicycle...
To corner at 1m/s/s, the front and rear must be generating 50N each of side force.
Case 1 - Neutral car.. where front and rear cornering stiffness (or really cornering coefficient) are equal, at say 50N/deg. To generate 50N each, the front and rear tires both would be operating at 1deg slip angle. Classically if we define understeer as (front slip - rear slip), the difference is 0 and at that lateral acceleration the car is neutral.
Case 2 - Understeer car. If we keep the same front tire, but now our rear tire has 100N/deg cornering stiffness... in our 1m/s/s corner the front will operate at 1 deg slip, the rear at 0.5 deg. Understeer = 0.5 deg.
Case 3 - Oversteer car. Front tire again stays at 50N/deg cornering stiffness, rear now at 25N/deg. For our 1m/s/s corner the front operates at 1 deg slip, the rear at 2 deg. Understeer = -1.0 deg (or 1 deg oversteer).
That works to describe vehicle yaw attitude. Limit balance will be dominated by roll stiffness distribution (among other things). Let's picture a 4-wheel vehicle now, cornering so fast that we're pretty much unloading the inside tires and the handling is dominated by the outside tires.
If you have a heap of front roll stiffness (relative to the rear) you will be dumping lots of load on the outside front tire. More load on a tire, it operates less efficiently, and it will use up all its grip faster than the rear -> limit plow.
If you have a heap of rear roll stiffness relative to the front, you dump lots of load on the outside rear tire. This time the rear is overworked and uses all its grip up faster than the front -> limit spin.
Grip is a four letter word.
2 is the new #1.