Except the issue isn't whether there are "dozens of other ways of buying things online, people just choose not to" but whether Amazon's market share is so large as to prohibit anyone from being able to compete with it.
Amazon sells ads on its marketplace. It also sells ads that integrate within its marketplace listings in a fashion that can be difficult to discern. It offers a fulfillment service that is integrated with its marketplace. It offers an integrated third party marketplace. These, are of course, facts. Whereas my initial response to was just the hypothetical point that you misunderstand how anti-trust law is applied. I don't think this has been much of a conversation seeing as how you are just being purposefully obtuse. It's clear you are making no efforts to come at this with good faith and I'm not going to bother any further otherwise.