A hard lick against the wall could leave a car essentially worthless, let alone multiple hits. Keep in mind that Forza 2 allowed multiple levels of damage, from cosmetic only to full... and even allowed for collisions to be turned off in online races. There's plenty of YouTube videos claiming Forza's damage system is bunk, but they've got damage set to "cosmetic" or "limited".
I hope PD doesn't let the Forza team out do them. What's so hard about non visual damage? Even some very basic non-visual damage like engine death for high speed collision would help the realism greatly.
I feel like I'm driving a car until I hit a wall real hard but then keep on going. At that moment the "realism" takes damage.