I understand it must be comforting to issue a blanket statement like that, but I it's just simply not universally true. I was hired on an E3, next job transitioned to H1-B and now have a green card. My work has directly enabled the hiring of three Americans. Is the H1-B perfect? Of course not. But on both occasions there were no other candidates, and when I was hired on H1-B I got a mandated higher salary to meet expected pay rates.