Other than the fact that the same team engineered both cars, I know comparing the Air to the Gravity for crashworthiness is apples and oranges.
But, for what it's worth, I can tell you that the Air is rock solid in a crash. Our first Dream Edition Performance was in a crash in which a teenager in an WRX turned left across our lane of travel. Both cars were totaled. However, in our Air there was no cabin deformity at all. All the air bags deployed, but every door opened and closed as if nothing had happened. We both got out of the car and walked away without so much as a bruise or a sore neck, then or later. (We replaced the car with an identical Dream we found on the used market and that we still have.)
@Amster was involved in an even more serious accident in her Air when her husband tried to pass on a narrow mountain road and an oncoming car sent them into a rock cliff face. The car was totaled but, other than his broken wrist (if I'm remember correctly), there were no significant injuries.
Also, our current Air with over 42,000 miles on it is still as solid and quiet as a tomb. By 10,000 miles our Model S Plaid was emitting annoying squeaks and groans from its hind quarters.
We haven't had as much time in our Gravity as we would like, but everything about the body structure telegraphs the same structural solidity we experienced in our Airs. I think your faith in Lucid's engineering team on this score is well-founded.