Can you post your settings screenshot?
There could be 2 reasons why you feel that way
1. If the return rate is too high, you might feel like you have to work the steering too much
2. If the limit multipler is too low, again you might feel like its understeering or nonresponsive.
So apart from increasing steer rate, try to:
1. Decrease return rate - to around say 50% of your steer rate
2. Increase limit multiplier to say 1.05 instead the default 0.80
But having said that XRG and XFG are no F1 cars and they have 720 degree lock, and these cars do not like sudden direction changes and you can't expect them to be too responsive, smoothness is the key.