Your experience is vastly different from mine.

I've worked at 7 different silicon valley companies in my 35 years of employment, though the last 20 have been at two particularly high flying companies. Approximate half the staff is foreign born, some US educated and most foreign educated. I see no pattern to skill levels between US born and foreign born coworkers. Maybe it is because these companies draw top talent, and can afford to pay for it, I have this experience. You might be cynical and think I'm a "meh" level employee who is easily impressed, but my pay grade and annual reviews say otherwise.