I don't really recognise the problem of excessive front grip. With a wheel, you can turn the front wheels beyond the point of peak grip, and it's difficult to turn them to the exact point of peak grip. Cars vary a bit in how forgiving they are when you go beyond peak grip, but I ended up going back to a controller after using a wheel in FH4 for a long time, due to how difficult it is to turn the wheel the exact right amount, vs the controller just automatically giving you peak front tyre grip.I am curious...who here actually plays Horizon with a wheel? I think it would actually help a lot. The fundamental problem (ie too much front grip, for whatever reason) isn't going to go away, but having precise control over the steering angle would seemingly make it a mute point.
It's easy to tune a car in FH4 to remove any hint of oversteer, but the meta is for cars to be oversteery, pretty much any tune you download by someone who is setting top times on rivals leaderboards will be oversteery, because if it isn't oversteery at higher speeds, it's leaving turning ability on the table at lower speeds. You pretty much have to just suck it up and git gud at controlling the oversteer if you want to be competitive in the game. You mentioned increasing front arb stiffness, but the meta is the opposite, max front grip min rear grip.