Some people seem to be missing the point and I don't blame you because brands are given a lot of protagonism in their announcement.
But I think the presence of renowned/popular brands in their announcement is just marketing collateral as part of a bit more complex marketing strategy that involved partnerships, and that might be confusing for anyone if deeper thought is not involved.
IMHO the essence of this product is neither about enforcing brand loyalty nor saving time.
1- Brand loyalty benefits well established brands, yes, so amazon probably got big companies on board by offering brand placement on their marketing material among other benefits.
2- Saving time (and cognitive flow/energy) benefits consumers, yes. There is some risk to follow brand reputation instead of product quality, agree, but that is a manageable risk, so amazon can potentially get consumers on board.
The essence and reason of why this product/service came to be, answers to one question only; 'How does amazon benefit?' and it is brilliant.
From my POV this little button is not just a way to introduce an enhanced experience to an existing and growing consumer behavior[1] that would result in greater sales for amazon; more than a product they introduced a service/platform[2] that can be seamlessly integrated to new home appliances, so amazon is effectively expanding its presence into a diverse and conveniently positioned custom/customizable 'points of sale' inside people's homes, making itself more and more ubiquitous as time goes by and more companies and individual innovators adopt their new service/platform, and their investment to accomplish this was little compared to the alternative of investing in manufacturing their own home appliances, but that's not brilliant, that's only natural and expected from a company like amazon.
It also places amazon's brand on not all but many people's minds as a high-tech high-quality home appliances brand by association to the actual home appliances brands, and amazon is not really manufacturing that kind of hardware (...yet), that's the brilliant part (an opportunity that they may or may never exploit, either because non-compete agreements or because it wouldn't make sense for their business plans or because Jeff Bezos decides not to because reasons, an opportunity nonetheless).
[1]: https://www.quora.com/What-is-the-future-of-food-delivery-1/...
[2]: https://www.amazon.com/oc/dash-replenishment-service