AWS is everywhere, but Amazon Retail is a separate entity and would definitely feel the crunch of even 30% of its users deciding to shop elsewhere or cancelling Prime.
(I cancelled my Prime membership a year and a half ago and do almost all of my shopping directly from manufacturers or from smaller stores. I spent thousands of dollars per year with them.
I used Walmart Lists to replace my Amazon subscribe and save purchases for a year but was finally able to, mostly, move off of that earlier this year. As it happens, HEB, a grocery chain in Texas, has just about everything I need!
I resisted doing this earlier because I thought I needed one/two-day delivery; I wrote posts on here defending this "need." It turns out that, no, I can wait a few days, and, yes, UPS, USPS, and FedEx are significantly more reliable than Amazon Flex.)