No...usually they fall in the bottom quartile as far as total compensation goes. That is exactly why companies like hiring them.
The "slave" part of it is that they are totally dependent on the company in the sense that they will be kicked out of the country if they don't follow orders, which usually means being overworked and underpaid.
I don't think you're listening. It's the law that companies hiring H1B workers must pay at least the average wage of the profession in the area. What are the sources on your claim that the companies are breaking that law?
The "slave" part of it is that they are totally dependent on the company in the sense that they will be kicked out of the country if they don't follow orders, which usually means being overworked and underpaid.