Walmart has very similar results to Amazon, just not quite as much, and limiting results to Walmart.com helps a tiny bit more. So I don't agree there.
You're mostly right about Target, they pretty much only sell stuff that they carry or brand themselves, but the other side to it for Target is that often you can't find what you want there at all - they have a pretty limited selection, and in any case the stuff they brand themselves just costs more and looks a little nicer, but usually it's not actually quality.
Walmart partners with their suppliers because they have a direct liability for selling dangerous or counterfeit goods. Amazon's lawyers try their best to shift all liability from themselves to their suppliers.
If I buy a product from Walmart that is faulty and injures me, liability falls on Walmart.
They still sell tons of stuff from the infinite dictionary of random import brand names that nobody's ever heard of like "Amplim," "Kootion," "Ktaxon," "Yosoo," "Zimtown," "Zokop," etc.
And Target’s website is painfully short on information about each product. To the point that sometimes there isn’t even enough info to tell what version it is so you can look up more details elsewhere!
Almost everything you'll find in either of those stores is made by a Chinese manufacturer that provides the same kinds of goods to multiple businesses. The store brands, especially, are essentially white-label Chinese goods.
It isn't a problem on Walmart or Target's websites, because they don't allow white-label Chinese goods to be sold on them.