I agree with your broader point about companies abusing H1-Bs. But I'm not sure if the abuse happens through hiring at lower wage. For example, if you look at FANG, they pay as much for an H1-B as they would pay any other employee. Where is this perspective that you can hire someone at lower wage because they come with H1-B? Would love understand the loophole.
You can work an H1-B nearly to death, Elon has all but explicitly said so for instance. If they're fired it's very unlikely that they'll be able to get a new job before being forced to leave the country at which point they're unlikely to ever get the chance to come back and they know this.
But this doesn't really happen in FAANG, as most on this board can tell you. Maybe in Elon companies, but they were well known for overworking everyone almost a decade ago
not every company is FANG. there are tens of thousands of companies operating at sub trillion dollar valuations which absolutely positively do this. FANG (or even "big tech") is far too narrow to draw any meaningful conclusions in the broader market.
Wages are not straightforward, as much as businesses would like to pretend they are. What do you mean by "would pay"? They don't just make up a number. The willingness of applicants to accept a lower wage lowers the wage they "would" pay ("our wages are competitive").
Most recruiters will do this due to avoid extra paperwork/work required. So now you know that anti-immigration rethoric is fueled by Americans to take advantage of the vulnerable.