Who is competing against Amazon or Walmart now?
The fact that you can plug Walmart/Sears/IBM/etc into it means there was something others were able to outcompete them on with even though the incumbent had scale.
For example, right now, I source my items from Costco/Target/Best Buy/Home Depot/Lowes/Staples/Winco (grocery store), Trader Joe’s, and I make minimal use of Walmart and even less of Amazon.
Also, look at it from the perspective of a small business. If you want to sell things online you're at a competitive disadvantage by not selling on Amazon. There are a number of companies that have cited this frustration. When you do sell on Amazon you're giving up some sales data which Amazon can then use to decide to undercut your product with their basics line, which very possibly comes from the same Chinese manufacturers at lower Amazon-negotiated prices.
Small businesses are also at a competitive disadvantage by not having the prime corner spot in downtown.
It just means you have to compete by selling something else that people want. If you want to play in the 2% profit margin cheap goods market, then you probably will not have a good time competing against others who have already optimized it.
Amazon has cornered the cheap goods online market (i.e. a more comfortable version of AliExpress). So do not compete with them on that if you want to earn more. If I am looking for something of decent quality, and you can figure out how to source it and guarantee that quality, then people will buy directly from your website (I do). Or Costco or Best Buy or another retailer will want to pick it up.
Oxo is another good example. They were able to expand their marketshare because they saw a market where people wanted to spend more to be assured of a higher quality good. Walmart was and still is selling the same stuff under the Mainstays brand, yet Oxo has grown because they correctly predicted that people would be willing to spend x% more for y% higher quality (or perception of quality).
To me it seems like this amount of commerce concentration can exaggerate existing economic disparities.
Anyway, I hope you're right and it works out well for everyone!
Amazon is a website, the cost of visiting a different website is pretty much zero.
The cost of not being on Amazon increases as Amazon's size increases. Is there a point where that becomes unfair?
In my opinion, not yet in the case of Amazon. As I listed, they numerous competitors, and one hardly needs Amazon to obtain their goods. It is trivial to throw up a non Amazon retail website.
At least I can think of many more businesses where consumers do not have an option and extremely high switching costs that need to be dealt with first. Such as a home’s wired internet service provider. That is an unfair advantage that needs the government.
I would say the iOS/Android duopoly is another big one.
The inconvenience of needing to go to a different website (which already exist) is not.
And to be fair: though Amazon seems unstoppable now, so did Microsoft, IBM, Sears, GM, Kodak, and many others.