Your starred assumptions may be better described as:
- The fungibility of mundane labor.
To wit: work that pretty much anyone can do with minimal training can be done anywhere by anyone. The “mobility” you note isn’t that workers can move, it’s that the work can - to wherever cheaper labor can be found.
I’m with you on the fungibility of mundane labor.
But, the jobs that are lost that are worth protecting, or phasing out slowly, aren’t (or weren’t) mundane labor—they were skilled.
Clearly the work can move, but the comparative advantage argument says that both sides are better off switching and specializing. But that assumes there aren’t any hidden costs. Look at the deindustrialized parts of the Midwest. Clearly there are some costs that aren’t accounted for in the prices of the various products that have shifted production locale.