You do not understand microeconomics. No economist would ever advocate for free trade in an academic environment. Competitive markets are the goal. The older I get the more I think microeconomics should be a basic course for voters. All the things you list “production capacity, efficiency, cost, and technical know-how” are well studied.

And you seem to be omitting that they won’t change given the demand won’t change.

In other words, people won’t just buy multiple iPhones just because it’s made locally.

I omitted it because I thought it was so glaringly obvious that it didn't need explaining: a factory owner doesn't care what the global or local demand for a product is, but at the demand for his factory's output. Which can increase, despite the consumer demand staying the same, if the competitiveness of other factories diminishes, like from tariffs.