In the real world, there are forces that a driver feels from the acceleration,
braking, cornering, or yawing (oversteer) that aren't present in a racing game.

Even without assists in the real world, a driver always has those forces that
can be felt and provide useful feedback.

However in a game, these forces don't exist, so having some level of assist
to compensate for the lack of forces might end up being more realistic than
no level of assists.

My experience with racing games is that a player mostly memorizes the control
inputs for a particular car and track combination, much more so that would be
done in real life. At the same time the real world car's response to control
inputs is changing (due to tire wear, heat, ...) much more so than any car in
a racing game.

The "perfect" simulator would probably be a remotely controlled race car.
The remote view would be the normal in car view. However I would expect that
that an external view might provide better feedback and result in better lap
times. At the extreme, a very remote external view, one that overlooks an entire
track, would might be better still, assuming headphone playback of the on board
sounds were used to eliminate any delay in audio feedback.

OK, now for a PC based racing game simulator? What, if any, compromises should be
made to make the racing game more realistic? The normal assists in current games
would always be available as an option.

In my opinion, modifying the physics to make the cars more forgiving when pushed
past the limits would help compensate for the lack of real world force feedbak.
This would include changes such as: more forgiving tire physics, reduce the rate
of yaw response (in most games, the rate of yaw response is faster than real life,
which is slower, even if not recoverable), modified audible feedback (tire scrub
sounds), and exaggerated visual roll and yaw response (some games include
adjustements for the visual stuff).