I have seen the Gravity at the Westfield Valley Fair but not sat in one. They wouldn't let me....in reality, the demo unit at Westfield didn't seem to have real 3rdrow seats, just mockups.
With respect to seating capacity and comfort, my main concern is, Gravity is 12" shorter (in height) than the R1S. The Gravity probably has a lower ground clearance. Still, I'd expect the inside cabin height to be 8:" to 10" shorter than the R1S. As I mentioned in other posts, both me and my son are 5ft 11 and we found the R1S 3rd row seat to be "comfortable" for short trips (say <2hr).
Lucid claims they can seat two 6ft 4in passengers in the 3rd row seat. That might be optimistic. I am sure you can get the passengers in there but I am not sure they want to stay there for a 2 hr trip.
I think the Gravity will do fine as a "Suburban SUV". It will be a step up compared to the Tesla X/Y 3 row. I am not so sure it is on the same level as the R1S or the Escalade.
If you can get me a free Gravity loaner to try out, maybe I will change my mind.
I hope the SW quality on the Gravity is a quantum step above that of the Air. To me, that's more important than the headroom.