Wouldn't you want the opposite? Once domestic production ramps up you gradually lift import restrictions to create more competition. I guess that's if the intention is to improve the domestic market in the national interest, rather than to just make people rich.

That is exactly what you never want to do under protectionist policies. Domestic producers are shielded from Chinese competitors. This means they are under less pressure to reduce prices and innovate.

I wouldn't read too much into the national security justification. It's a political argument to an economic policy.