First order effect might be a benefit to consumers, but this kills competition. Those brands and products that amazon copies could eventually die out, and now there's less competition in the market and less forces for better products for customers.
Do we have any evidence of this? Walmart still sells non-great value products (started in 1993!) while I get why copying a niche product might cause the original manufacturer to die out and if there are examples of this I am more than willing to change my opinion.
If you actually take a look at their offering (https://www.amazon.ca/-/en/stores/page/BFAE3282-E15B-47EE-90...), most of these are legitimately "basics", things that existed 50-100 years ago. Wilson won't die out because Amazon sells a volleyball, nor will Duracell because of offbrand AA batteries
