Plenty of ventures back by big names end up dead. Even when Amazon or GM themselves execute a new product, it's no where near a guaranteed success...
Tesla has products and paying customers. Big difference.
Tesla has products and paying customers. Big difference.
Amazon no doubt wants in on the self driving electric vehicle market to compete with Tesla, Apple and Google and heavily investing in the best EV startup other than Tesla is the easiest way into this field. But because of this I would put Rivian as only slightly behind Tesla.
Now you are right, forcing your way into a field by throwing money at the problem doesn't always ensure success, just as Windows Phone. But as with Windows Phone it does usually ensure a decent product gets to market. And that is all I am saying will happen. The likelihood of a Rivian product getting to market is just as likely as a Model Y getting to market. Both extremely high.