They could change the way custom races payout. The way people overused it in GT Sport was because in a race of just 2 cars, where you put your Miata against a Gr.1 Car and rubberhand it against the wall in an oval circuit, the car that came in 2nd, ergo, last which was obviously your Miata, would still get paid a ridiculous amount of money for a long-endurance race. Something in the millions.
PD could've easily fixed this by not giving any credit prizes to the car that comes in last place, which is only fair. And thus pretty much negate the ability for you to just cheese through them to earn easy credits.
Instead, they went to the other extreme, where a 24 hour custom race where you eventually win, on same category cars, pays out... 400k. Which is about enough to buy a Porsche 911 GT3 RS and not even fully tune it. Pathetic.
Sport mode was designed for just competition. However, they could've brought even more people into it to enjoy themselves while also trying to earn some credits.
In Sport Mode, you 100% cannot cheese your way to win, if you win, its because you were good/fast enough to do so. So how come you get prized something like 25k credits for a race win against real life players that are supposed to be on your level, which is of course, far beyond what the AI in the game can do to compete against you?