But either Amazon will have the product or it will still be valuable to another middle man.
Amazon have a lot but are a long way off having everything. Health and Beauty for example, they may have the top 50k sales ranks pretty well covered but at least the top 100k are probably worth a middle mans time.
Not all products are really valuable to a middle man. From my insights regarding Amazon sellers, ~70% of the profit is made from ~5% of the products, and those are the products Amazon is taking away from them. If they then only have the low-profit items remaining, they aren't able to be profitably on Amazon anymore, unless they operate at significant scale - a scale that becomes very hard to grow to when Amazon is constantly taking away your means to do so.
Amazon have a lot but are a long way off having everything. Health and Beauty for example, they may have the top 50k sales ranks pretty well covered but at least the top 100k are probably worth a middle mans time.