I'm sceptical of the claim here, in that I don't think American-made variations of items would magically appear in a protectionist world.

The reason American companies don't make certain things is because the return-on-investment isn't favorable due to all of the laws and taxes. Adding importation barriers wouldn't change that fact.

This was proven in Brazil when the government implemented protectionist tariffs; Brazilian companies didn't suddenly spring up and make PlayStation 4-equivalents-- rather, Brazilians were stuck playing thirty year-old video game platforms.

To put it another way, the alternative wouldn't become "simply buy a slightly more expensive, home-built good"-- it would be "don't have that kind of item on the market at all."