I'm sorry but controlling 911 cup car with throttle is not that realistic,
I have seen many many drives specifically saying power on understeer in the porsche 911 , even in street cars.
for example i remember chris harris reviewing 911 gt3 road car NOT even RS version on cold damp conditions with street tyres below their optimal temperature range. he said that porsche struggled to get rear end out even in 2nd gear corner
Look at 6:15 in video below >>
This car has significant aero boost and similar power compared to old 991 ,fatter rear tyres better suspension etc etc, so grip to power ratio is worse....i.e even harder to get rear end driven by throttle.
Especially in gear above 2nd.
Your best bet is to take away lateral grip, run stiffer rear ARB than front zero rear toe ,less wing (which will be slow as this car has low drag, low top speed you ought to utilise more rear wing).
In short what you described, perfectly matches what i heard from many actual drivers and this is what i expect.