If I want to buy a widget and I'm looking for the one rated best or cheapest or whatever, why would that rating be affected by (a) how big Amazon's selection of products is (b) how good Amazon's customer service is (c) Amazon offering free delivery.
If you SORT your search results by "Price: Low to High", you will still see the lowest-priced sellers first, and when you click-through to the item, will be offered the lowest-priced seller. Of course Amazon's site is still crap after all these years, and shipping cost is NOT included with that, but still.
It's only if you DON'T sort by price that Amazon will use numerous metrics to decide which seller to feature for that item listing.
I've absolutely seen Amazon NOT featuring itself, when they have the item available, but other sellers have the item for a non-trivially lower price. When that doesn't happen, it seems to be because the cheaper seller has a poor seller feedback rating, or else is new enough to have little or no feedback.
Your A, B, and C are absolutely relevant, in those cases. Most people don't want to hassle with some unknown merchant who might send them counterfeit crap, might disappear and refuse returns or fail to issue refunds, and it's also usually a benefit to spend a few cents more so that the item adds to your free-shipping total, or else can come with 2-day Prime shipping, if you are a subscriber. Amazon is almost always a better choice in those cases, for those reasons. How much of a price-difference that's worth is debatable, but you can do a couple more clicks and find the lowest-priced seller for that item, instead of accepting Amazon's judgement for you.
Sorry for interrupting. You may now resume your insane and baseless rant against "the man". I'd like to preempt the paranoid ranting by stating I have no connection with Amazon, other than having been a heavy buyer for a few years, and just observing over a long period how their mess of a system works (and doesn't).