Well, the 1- and 2-day service with no order minimum is a huge part of the package; you can't just put that aside. And you get a pretty good video streaming service thrown in as well (which has enabled me to watch The Expanse, for which I am grateful).
All I'm saying is that Amazon isn't secretly sliming you with their free shipping, at least for products that *they* sell (vs. 3rd party sellers). They are an inconceivably large operation that has various ways of making back that money. They are not always cheapest at everything, but their prices are generally very good, and they are a very easy one-stop-shop to buy stuff, especially once they have hooked you in with Prime.
I am not saying anyone should or shouldn't buy from them.