No current racing sim does accidents very well. GT is worst at it as you describe. As for car handling physics. Few games come close. As shown, by your only complaint being how the game handles accidents. Forza doesn't.
Games like GTR2 are a set above GT, as they simulate many more aspects of the car.
It's not just dramatic head-on collisions with stationary objects (which GT is laughably bad at), but also
much more frequent and important car-on-car collisions and bumps, which is
atrociously bad in GT. Slamming into the read end of a car at 85 mph because they suddenly braked does nothing, nada, ZIP, to you or the other car. It's laughable. At least in Forza, it causes a spin-out.
And with how terrible the AI is, bumping into cars, and having random AI bump into each other, is an issue that can't be overlooked.
Either way, Forza's modeling is still light years beyond GT's in that aspect, and at the very least quite reasonably close in other physics aspects.
The one thing where it's not even close, is how soundly Forza
trounces GT in virtually everything else.