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He is. Like most robber barons, I'd expect his empire to crumble at some point. Amazon is essentially a 21st century Sears. It owns and operates a lot of different entities that don't appear to fit very well together and has so many focuses that it's hard to know what the company really wants to do.
Does it want to be a retailer? A grocer? A technology services company? An entertainment company? An insurance company? A logistics company?
Amazon's signature acquisition, one that that Wall Street is in love with, is an overpriced, over hyped, rudderless specialty grocer that was quickly losing its footing in the market. It's website may be the easiest place to order almost anything but it's not the cheapest. Amazon also isn't very fun. Looking at a photo of an item on a screen (oftentimes a tiny mobile screen) and then clicking "buy" just isn't the experience that walking through a store and looking at items is.
He's being helped, in part, because we're beginning to suffering from the effects of the aggressive, over expansion of traditional retailers in the 1990s - early 2000s. The problem was that the market was never able to support this massive expansion (the older locations were generally kept open when the newer locations opened up, and they cannibalized one another as well as the newer centers cannibalized the older centers).
Weak chains that over-expanded during that time such as Circuit City, Linens N Things, and Mervyn's are long gone. I'd also put Toys R Us, Sears, and Kmart (at least at the early part of the 1990s) in this category.
Stronger chains such as Macy's, Kohl's, Sam's Club, Target, and Walmart are also suffering from some poor real estate decisions, over expansion, and declining demographics at some of their older locations. Also, of the bunch, only Target appears to even be trying to cater to urban millennial (and its offering is weak at best).