I think it’s fair to say that there are very skilled foreign workers, and there are average ones as well. Same for the domestic workforce. In my line of work (scientific research) the head count is about 50-50, and I don’t see substantial difference in quality between locals and imports. True, there are some cultural differences, but these tend to fade out the longer the people in question stick around here.
The fact that these people are here at all proves that there are more jobs than qualified local candidates. You can take this either as (i) an indictment of our education system, or (ii) a sign that American companies are doing very well and are atracting talent from abroad. I think both theories have some truth to them.
