I believe Walmart will eventually succome to the same old age diseases that got Sears.. Please remember that Sears was BIG, selling everything from houses to farm tractors, for awhile automobiles, ( remember the "ALLSTATE" which resembled the Henry J?), their own brand of high quality firearms, musical instruments, clothing, tools, and everything except groceries.
After 75 years or so, the management got greedy and were soaking up the profits by paying themselves ever more and doing less and less until the "dime stores" such as Woolworths, Kresges and the like had room to slide in underneath them with a lower paid and more energenic work force and their "day" lasted 40 years or so.
Watch organizations like DOLLAR GENERAL, COSCO, DOLLAR TREE and WALGREENS slide in under Walmart. As to having a superior business model, it is now the norm for everyone.
Remember the old "fair trade" laws which were designed to prevent near monopolies such as Walmart, Microsoft and the like? They no longer exist. Whether their existence benefited the consumer or not is still argued in economics classes.
Speaking of the merits in old laws, consider that for a very long time milk production was controlled to ensure a steady supply. "Boom or bust" doesn,t work very well in the dairy industry because of the long time it takes to raise a producing cow. Right now there is a milk surplus, and lots of milk cows are being made into hamburger, and soon there will be a milk shortage.