I wouldn't agree that a negative cash cycle is outdated. However I would disagree with the author's inference that a low profit business with negative working capital is as good a high profit business.
As evidence, I'd point to a great negative working capital businesses. Dell. No one's arguing that Dell is a super business thanks to the cash it generates because of its negative working capital cycle.
Bezos is obviously brilliant. It's possible that he made the decision to stick to low margin businesses because he knows that won't attract competition. That would be counter-intuitive and pretty brilliant if you're certain you can out-execute your competitors in the low margin space.