The brake balance controller has effects when it should not. It causes oversteer and understeer according to the settings when you are decelerating, but not using the brakes.
The FC RX-7 series all handle nicely.
The FD RX-7 are sensitive to ride-height being lowered too much, and sudden oversteer which, AFAICT, can be practically eliminated by keeping the brake balance controller at 11/11. I.e. moderate and balanced.
The NSX can be tuned to be controllable, too, but remain somewhat quirky.
I have won the Hard Tuned Series with both the NSX'91 and the NSX'93.
Stiffer rear dampers help prevent exit oversteer, and the extra entry oversteer created seems neglible. So using stiffer rear dampers often helps get quirky cars, especially over-powered ones (which neither of these candidates are, really) under control. The damper seems to be more of the "rebound" than the "bound" setting of the later games.
I can try to look up some settings to try.