The bottom 50% has gotten fucked by loss of jobs/industries/career paths/debt, but H1Bs aren't helping with that.
So if your contention is "we need to figure out how to better invest in the whole population" I agree, but I don't see the other half of the equation being an overly large limiting point.
If anything, if we're in the lead industry-wise, does importing young talent, teaching them these things, and making it easier for that experience to be taken elsewhere really help long-run? Almost sounds more like a case for paranoid isolationism immigration-wise.
We're never gonna have a billion people in the US in my lifetime, but I don't think that's necessary for there to be enough US self-driven industry to have a nice, happy, productive life.
There's a gap in China as well but it's made up for by a massive population. Lord forbid they close their gap, that'll be the end of any other country's ability to compete as China and India just throw five hundred million engineers each at their technology sector.