So the US underinvested in the native workforce and now the chinese have gone back there's a big gap that a native workforce would have filled if they hadn't been temporarily replaced by chinese? Seems terrible short sighted.

Yes. The mechanism is that American kids stopped learning useful things like STEM skills. I remember when I went to college in the early 00s, every single person in my physics class was either an immigrant, child of an immigrant, or Jewish. Now we have a shortage in engineering skills that has to be filled by H1Bs, and a population that all gets service jobs and consumes disproportionately because of an overvalued reserve currency. If that currency ever stops being overvalued, we're fucked.