I suspect you are an outlier. Amazon takes ~50% of online shopping market share [1]. Admittedly it is lower than I thought. I expected it to be closer to 70%. Google for search is actually at 71% [2]. Either way, I think 50% is enough market power to be treated as a monopoly, not sure about the legal definition.
That said, I am not particularly worried about Amazon basics as these are commodity products, as long as they are being transparent about it. Monopoly is a problem only if they use tactics that prevent competitors from emerging - example could be incentivizing vendors to sell only on Amazon.
Taking 50% of online shopping share because your product is that much better than the competition is totally different than there are no other options.
Imagine you have 1000 stores all on the same street and one is so much better than the other stores that 50% of sales happen in that one store and there are no shenanigans where that one store is disadvantaging the other 999 stores. How can you argue that that is a monopoly?
That said, I am not particularly worried about Amazon basics as these are commodity products, as long as they are being transparent about it. Monopoly is a problem only if they use tactics that prevent competitors from emerging - example could be incentivizing vendors to sell only on Amazon.
[1] https://www.statista.com/statistics/788109/amazon-retail-mar... [2] https://www.netmarketshare.com/search-engine-market-share.as...