Sure, but I don’t think supply chains are the critical factor here. You don’t necessarily need local supply if you can break up delivery into small enough chunks, so whether it takes a day or a month to get a part isn’t important once the flow is going smoothly. You only need local supply if there’s a significant risk of disruption/delays.

Yes, it’s probably a bit cheaper to assemble things closer to where they’re produced, but I still think labor costs are the determining factor. US workers expect higher pay, more PTO, less hours worked per week, and more benefits, so even if all the parts were shipped in perfectly consistently, it would still be significantly more expensive to assemble iPhones in the US vs in China.