When you turn off the ASM and TCS systems in GT os when the truly "real simulation" happens. Those systems are on by default in GT to make it easier for the non-hardcore users. As they progress through the game and gain more skills, they'll then be able to turn those off and race with more realism.
Forza is just ugly in every aspect compared to Gran Turismo anyway, and the damage simulation is always either too much or not enough.