I would argue its about improving labor productivity. What you are saying is American corporations want labor with higher productivity and even willing pay more

I would argue its about improving labor productivity. What you are saying is American corporations want labor with higher productivity and even willing pay more for more productive labor (by paying immigration costs). Thats why SWE salaries overall increased and H1Bs are making the same salaries as citizens, because of higher competition leading to higher productivity. Importing foreign workers (and culling bottom 10% via forcing curve/pip) forces average labor productivity to increase