I would go further and say that underpaid H1-B's are a straw man to the real mechanism that depresses American wages. Even if imported workers are paid exactly

I would go further and say that underpaid H1-B's are a straw man to the real mechanism that depresses American wages. Even if imported workers are paid exactly market, that still means market prices do not go up as there is no one to bid up salaries. That means people are not being compensated for delivery high value, or for developing skill in a difficult or rare area. There is a lot of hot air between the salary a person would accept versus the value they generate for a company. Having some unemployed people makes it so that the balance always tips towards the low end.