What if H1B workers became free agents after 6 months? No paperwork on the part of the hiring company, they just accept a new offer and file something to say they are switching employers. If the problem is that there are not enough qualified people in the "hiring pool" then this shouldn't matter, right? After all they will tell you that they're paying a competitive salary already.
This whole artificially depressed salary thing could blow over if they weren't indentured servants, unable to move. You could normalize salaries pretty quickly. And the sponsoring company would have to become competitive enough to keep people.