Imagine the grip you could get if the back wheel was the entire width of the vehicle. The main grip would still be on the outside, but you could make the "axle" non-rigid so it could flex to have more friction on the road. Yes, it would require more power, but it's not too hard to make 1000 HP power that could still spin the back wheel.

In the past, I assume the limitation was getting the power from an ICE power source to the back wheels in absence of a traditional power train. Nowadays, with electric motors getting so good, internal hubs would simplify the problem massively. Imagine the acceleration and turning ability. Top speed would be reduced, but depending on the track, you could probably get faster lap times than standard 4 wheel setups.