I have a rivian, and my wife has a car with carplay. I've had rivians for years now. I don't miss carplay when i drive my Rivian.
In truth, I used carplay for 3 main things - navigation that didn't suck, listening to music on the apps i wanted to, and reading text messages out loud.
Rivian has made those things not suck. So i don't miss carplay.
On my wife's car, those things suck, badly, without carplay.
I'm sure there are people out there who heavily depend on carplay for other things, and thus, it really does matter if they have carplay or not.
and maybe a day will come when the features carplay could provide me are as shitty on the Rivian as they are on my wife's car, and i'll start demanding it again.
But at least right now, that's not true, and so I think Rivian's choice is fine.