For a properly sorted GTR you don't need to trail brake into any corner, just full throttle around the corner mate
If your car understeered then either you did not get on the throttle early enough, you are taking that corner too fast or your car need another appointment at the wheel alignment shop.
What you guys are describing is possibly due to poor wheel alignment or worn out bushes. A properly working hicas system will make the car turn in better and feel a lot smaller. It's only a problem if you have too much power (320+rwkw) and try to control the car with most of that power around the corners. The last thing you need, in this case, is some extra changes in the rear wheels during turning.
Another factor to take into consideration is that the GTR needs good tyres. If you have poor rubbers then it is the same as driving a high powered car around corners (just with a slower corner speed). Removing the hicas in this case may help but you are really chasing your tail rather fixing the problem.
I've driven 320rwkw cars with proper suspension setup and still has hicas. The car still feels so good around fast corners.
My track car has much more power than this and the hicas is disabled.