It strikes me that a lot of the talk around 'understeer' and such is connected mainly to two things, one is a change and one is a carry over that is impacting the other changes...
1. People driving Gr3s with BOP Fixed setups. These setups are absolute junk. This is why there are 'meta' cars for certain tracks because PD applies the same setup perimeters to ALL Gr3 cars, meaning that it will suit some cars everywhere and some nowhere. They put a lot of built-in understeer to make them 'safe', so when the other physics changes come in that have affected the next thing I'll mention, they make them even worse in that regard...
One of two things can be done to address this. Petition PD to update the setups, or petition them to remove the suspension/downforce figures etc from the BOP calculation and make it a weight/bhp thing, opening up those perimeters to driver adjustment. I've mostly stopped racing Daily Races because of this, and the league racing I do on GT7 we use the bhp/weight BOP figures with open setups for everything else (it's a shame there's no way to apply this within the game, so we operate on a trust-based system for this).
2. The aerodynamics seem to work much more realistically. Downforce bleeds off the car when the speed lowers, so if your car is mechanically setup for more understeer, as soon as the mechanical grip becomes more important, this will be where you feel this. If you experience understeer in medium or higher speed corners, this is a problem with your aero balance. You might need to reduce your rear wing levels.