I HAVE seen a prime example of that. I've also seen some workers from India that were in fact pretty good at what they did. I definitely wouldn't say that they were superior to American engineers however. The ONLY advantage they have over American workers is that they work for less money, work longer hours without complaining, and can't quit.
When I worked at a large Bay Area computer company they went in for the big H1B influx. It was pretty funny. One outspoken engineer, a staunch Dem, called them scabs to their face, told them point blank they were here to lower the prevailing wage, refused to "mentor" them on anything, talked to "60 Minutes" and got them to cover the H1B story and in general was the biggest pain-in-the-ass imaginable on this whole topic. He was way to valuable to fire, and he knew it. Management was very upset with him, but I kept quoting the "employee handbook" back at them in our manager meeting. Pointing out that "open communication" was a "core value" and the company encouraged political activism. As far as I know he still works there.