[sandoooo]

Building slack into the supply chain would be a very inefficient way to stockpile for emergencies, compared to actually stockpiling for emergencies. As you've said, it would make no sense in the case of the iPhone. The McKinseys of the world are absolutely right about this.

The problem is that the old system created a positive externality (coincidentally storing a bit of inventory for emergencies, though inefficiently and in no way planned) that the new one doesn't. It's the sort of thing that should be fixed by government incentives.