To be clear, you disagree because you fundamentally don't understand what's going on. I'll explain it to you.

A company makes a product - it costs $10 per unit to make. To list and sell with Amazon, they are charged $12 per unit. To make a profit the company adds and additional $1 per unit. They sell the product on Amazon for $23 per unit.

Online retailer Foo also has a store, and provide the same services that Amazon for their online shop at $5 per unit. The online retailer adds a profit of $2 per unit. Total price $17 per unit. Retailer Foo is more $ efficient for those services as a result customers price compare. Foo is rewarded for their effi with higher volume, manufacturer is rewarded with higher profit and consumer is rewarded with lower prices. Enforcing market competition led to all 3 parties involved being rewarded. Retailer Foo over time grows a larger customer base as people learn to price compare with them and forces Amazon to stop rent seeking.

But the above doesn't happen in the real world. Amazon enforces that the retailer lower their price on Amazon to $17, while still collecting $12 per unit. The company now can sell on foo, but only by selling on Amazon at a loss. They can't afford that amount of loss from Amazon and stay in business. So Amazon avoids competition. They can't pull their product from Amazon because not enough customers vist Foo retailer yet to make up the volume.

So in the end Foo retailer is more dollar efficient, but is prevented from growing and benefiting the marketplace. Amazon leverages its outside market size to avoid competition. Market participants preventing competition is against the benefits of capitalism and harms the consumer. So, it benefits the consumer to ensure Amazon has to actually compete with the more efficient competitor and stop rent selling behavior.

I do understand, but what you're describing is bad for Amazon's customers, as you note yourself.

Furthermore, again, no one is obligated to sell with Amazon. There are thousands, if not tens of thousands of sellers who do not sell their stuff on Amazon. It's not some requirement to do business in the 21st century.

In any case, we can come back to this case a year from now, and we can pretend to be shocked when nothing meaningful happens to Amazon.

I think you're looking at the short term and small scale instead of the long term and large / societal scale.

Yes I'm the short term Amazon's customers don't get the discount they could get om Foo retail. Bit then they become Foo retailer customers and they benefit. Too many things optimize for the small scale.

Similarly Amazon's upon losing customers to Foo retailer has to become more efficient overall (or reduce its rent seeking fee) to stop losing customers. So now all of Amazon's customers for that product benefit, even those that didn't move. And potentially even those customers for other Amazon products.

This is the purpose of capitalism - marker competition. Nobody wins with laisse-fair capitalism except rent seekers. Society benefits from market competition in capitalism and this is pushing for it.

You must be aware that producers can sell their own product and not be dependent on neither Amazon, nor any other middle man.

If I make light bulbs and sell them to customers through my own channels – exactly who is the rent seeker?

In my industry there are actors that are as dominant as Amazon are in retail, but there's also a huge part of the industry who just sell directly to the customer. It's your own choice. If you don't accept Amazon's terms, you don't have to do business with them. And vice versa.