Apple doesn't make any money off physical items sold through the Amazon app. The 30% you're talking about only applies to a digital purchase to be used on the device itself. You may indeed know this, but in your arguments you keep describing Apple's 30% cut of Amazon purchases in very general terms which could mislead readers into thinking you're talking about all purchases from Amazon on the app.
So if you think this is the case, how does it work? If I have a subscription to Netflix, that's a deal I have with Netflix. When I watch a movie on the app, how do you think Apple takes a 30% cut? Specifically, does Netflix hand over 30% of my monthly or annual subscription fee? Do they prorate my monthly or annual subscription down to a per-movie rate and give Apple 30% of that rate? If so, how do either know what that rate would be, since neither Apple nor Netflix know how many movies I'm going to watch in a month or a year? So I'd think prorating would be impossible.
I'm asking specifically what this supposed 30% cut on Netflix you describe is based on. If you have that info I'd love to see it.