And once you look global, there's plenty more 100B+ revenue retailers, many of which also sell in the US.
I hardly think there is even close to an "absence of competition." Heck, Amazon is not even the biggest US retailer by a large margin. Each of these posts is full of fear and implications the evidence and statistics show to be unfounded.
[1] https://nrf.com/research-insights/top-retailers/top-100-reta...
I think you misunderstand the reasons prices actually become lower for many goods over time. Or why some producers get replaced over time by more efficient producers. Without this process there's be no lower prices or more efficient production over time.
Do you call this "efficiency"? How many companies in the world can afford it?
[0] https://arstechnica.com/tech-policy/2020/07/emails-detail-am...
The proper way to asses things is not to post select evidence, but to pick every example of price lowering at a given time, and see how many become the situation you now describe. So, care to tell us what percent of price lowering incidents end up as extreme? I'd guess well under 1 in a million, but I may be off an order of magnitude in either direction.
By your reasoning, every time a person enters my house I should inform them they may kill me, since once in a while a person does enter a house, then kill the occupant.
However, I'd be a nut to act this way. Because the vast majority of cases does not end up in murder.
So, just like that, bringing up extreme cases for normal actions is also fear mongering nonsense. Yes, this could end up tis way. They could use this as a leverage point to take over the entire planet, enslave all humans, and turn us into Matrix-human-batteries. But continuing to harp on this as if any of it is likely is statistically unwarranted.
So, please answer - what fraction of price lowering events do you think ends up in the situation you keep implying this might be an example of?
Diapers.com is just an example.