Where I work, they're filling roles of what would have been called an engineering clerk, back in the old days. Jobs for which a BS is an over-qualification. The visa holders are vastly underpaid for their education level, while people who would be a better fit can't get their foot in the door, and get a huge boost to their income, because they don't have a degree.

I think the "as we all know" is that big corporations use the visa program to create, in essence, indentured servitude. People who work for far less than the market-clearing wage for the position, because are beholden to their corporate sponsor. I find it reprehensible, and particularly galling that it's all done in the name of "diversity."

Most visa holders are young and incredibly vulnerable. Combine this with my particular company's absolutely legendarily capricious hire-and-fire cycle (for 30+ years), and they can really stick it to immigrants working for them via subcontracting.