I might be misinterpreting the article, but the first two paragraphs specifically describe the over-abundance of marketplace sellers offering similar and sometimes identical products. They're using the same seller platform - Amazon - but that doesn't seem the same as lacking marketplace options as a consumer.

Not sure if it's a perfect analogy, but if we compare the Amazon marketplace to a giant flea market, I think the claim that consumers need a reasonably high level of 'savvy' to operate effectively is pretty easy to defend. When there are lots of sellers, lots of noise, and difficulty verifying quality, the consumer will frequently lose out despite the surplus of marketplace options.