There is a stronger case against Amazon for selling Amazon-branded, well-moving products like batteries and diapers, even though they don't stifle the other brands.
Having had to take antitrust training at my company in the past few weeks, I can say that you are very mistaken if you think antitrust only kicks in when the company is a monopoly.
You can fall afoul of these conditions if you have "sufficient market power", which is a substantially broader claim than "monopoly power." I don't think there's any lawyer that would try to claim that Apple doesn't have "market power"--note that the smartphone market, from an OS perspective, is basically a duopoly.
Both Hulu and Netflix compete directly with Prime Video, and both 1) are available as free apps for Kindle and the Amazon Fire Stick TV and 2) literally rely on Amazon hardware to run through AWS.