Forgetting about the exact weights for just a second then you are totally correct. If you use thicker oil than optimal then the oil will slow the transition down causing the car to lean one way while you are already turning into a corner in the opposite direction. The faster the car goes the bigger this problem. The solution then is indeed to go to softer oil or harder springs.
With foams this is especially true as due to the high grip corner speeds are very high. Quick transitions are key. This is exactly why with foams we run the same weight oil with hard springs that we run with rubber tyres in combination with soft springs. Having said this, a bumpy track will require more damping which then obviously will come at the expense of slower transitioning. BUT, on a bumpy track your car will be slower anyway unless you are Evil Knievil
