Having both a tesla and rivian, rivian has a better software/interface. I feel like carplay is great if you have a 5" screen. For these full screen vehicles, a much bigger interface is needed. Would be cool if it had some carplay ultra features, but can see why they don't use it.
Tesla has better self driving
Rivian has better interior and UX
Pick your poison
Side note:
Scout could be the coolest EV brand if they could launch with carplay ultra and if their vehicles look as good as the prototypes.