Unless you moved the cars center of mass up or down, it's impossible to have changed the amount of chassis-rotating force the mass of the car would exert in a corner of a constant G. What may have been changed slightly is the Y-axis polar moment of inertia, meaning that the energy that the car uses upon entering a corner to first accelerate the chassis Y-axis rotation, which once moving (twisting) the speed and inertia of the movement is slowed by your dampening and then, once maximum cornering G has been achieved for a fraction of a second, stops being relevant as the car has completely set-up and there is no movement in the suspension. At that time all of the potential energy which upon exiting the corner or slowing down will be used to uncompress the chassis back to flat has been absorbed by your springs, an energy quantity independent of the polar moment of inertia and dependent only on mass, height of the center of gravity, and cornering force. So overall, changes to that moment of inertia will mean the car requires less energy to compress itself into a turn and spring itself back from cornering forces, but the force exerted on the side spring at constant G will not be changed. Technically you could say that the reduced rotational inertia to be absorbed by the dampening system would reduce the chances of over-compressing the side spring and over-rotating, but there is no 1/12 scale car in service today that isn't far massively overdamped in terms of its pendulous motion. Another argument would be that because there is a greater inertia to be absorbed by the side dampening in a given amount of time that this could result in momentary over-loading of the outside rear tire upon entering a corner from the greater dampening, but I cant say if that momentary force is good, bad, or indifferent for the car's performance.
On the other hand, you HAVE increased the energy the car will require to rotate itself on its X and Z axis, meaning that weight transfer from front to rear will be slower but contain more energy, and the energy used to rotate the car itself will be increased, there is a tradeoff to be accounted for here, and I don't claim to know the answer but I have decent reason to think that none of these values have changed more than a few percent by turning your battery sideways and then mounting your heavy brick of a speed control, receiver, transponder, booster, or receiver pack next to it. I think I can safely say that it is not just "Less side roll is achieved" or "faster in the turns."