I understand the issue well enough. When you're talking about H1-B subcontractors being paid less, my response is that it is commonplace is all of the industries that have increased their use of subs.
I wrote an entire other post about the claim that it's not being effectively used and has unintended consequences and how that claim isn't really valid. The businesses are using it as intended. The visa holders are using it as intended. Those are the 2 groups covered by the program and they both seem to using the program effectively for their needs. Your complaint is about the domestic workers, but they were always going to be negatively impacted by the existence of this program, that's not an unintended consequence.
If the claim is "the increased use of independent contractors are undercutting employee wages", that's a reasonable position to argue and one I would agree with. If the argument is "H1-B's specifically need to be revamped because they're undercutting domestic labor wages," that's not a position I would agree with. It's missing the forest for the trees.
It's not H1-Bs that are hurting domestic labor in the IT. It's the increased use of independent subcontractors that are hurting employee wages across all industries, which includes IT. The form of the independent contractors, whether it is through these H1-B mills or through something like Uber or contract attorneys or contract accountants, doesn't matter. There is a structural shift going on in the form of employment and constricting one's approach to the issue to a narrow facet of a single industry really, really misses the point.