As long as Amazon “investors” keeps supporting many of Amazon’s money loosing operations, they’ll remain hard to compete with. And who cares? If someone wants to support you by splitting the cost of your purchases with you, why not let them?
The important thing to focus on, is to ensure that no matter how big Amazon gets, and no matter how wealthy Bezos gets, the government will never, ever in a trillion years help them lock in advantages their subsidized growth has enabled them to attain. Meaning, no patentable processes, no exclusives, no special deals, no nothing. So that as soon as the subsidization dries up, anyone can just copy whatever Amazon is doing, perhaps improve it a bit, so that the competition will prevent Amazon from ever being able to rent seek by raising prices above a purely free-for-all competitive level. Things that truly does get more efficient with scale, will still provide areas where Amazon has an advantage. But nothing else will.
The US is probably too far gone down the road of a lawyer , bankster and “investor” centric corruptopia to prevent our largely and increasingly totalitarian regime from tilting the playing field in aid of the big and wealthy to the detriment of everyone else, domestic as well as foreign; but other countries should in no way be dissuaded from, heck should be encouraged to, treat most US intellectual property legalization as what it is: A steaming pile of manure, existing solely to aid a gang of useless, unproductive wastes of space in robbing productive people of their output and needy people of the stuff they need. The more thoroughly it’s all disregarded with abandon, the better.