I, for one, don't think CarPlay is "the end all be all". Plenty of downsides. But, it's what I use, for several reasons. One of them being that I regularly drive three different cars of three different brands, only one of which is my own. Being able to just connect to Carplay and use everything the same way (more or less), is very convenient. This is just one argument, not THE argument.
But no, I haven't tried a Rivian. It's not really the style of car for me. But plenty of people are trying to convince me that Tesla's software is so good I won't miss Carplay - and after driving one, I simply disagree.