As to the question, I would guess the answer is "Not easily." Otherwise, we would not be having these problems with overgrown websites acting as middlemen for large swaths of the web. The rest of your statements are all true, but that does not change the truth of "They simply lack the web traffic". Amazon has an amount of traffic that gives them leverage as a middleman.

Beyond that, even when you order directly from the manufacturer's website, that doesn't mean they, personally, are handling the sale. All the logistics that go with fulfilling orders and customer service around that I'm sure is outsourced frequently (to Amazon or someone else)

True, however those payment processors are not in competition with the sellers in terms of the goods/services being sold.

The facts are that Amazon does not sell only payment processing, order fulfillment or customer services.