> Amazon is offering a big open marketplace where they invite people to offer goods, then they observe which goods sell well and how are they made, then the push out the sellers and they offer their own versions of it, essentially pushing the risk onto sellers and only reaping the benefits.

But this is exactly what is done at innumerable retailers like Walgreens and Safeway. The retailer is a "marketplace" (they sell multiple brands for each product) who controls "search placement" (where each product is displayed, e.g., eye height vs. near the floor) and have insider information on how well the different products sell. They use this advantage to make their own knock-off brands, and its generally a win for the consumer.