My personal experience working with visa workers at multiple organizations is that many organizations do indeed use them as de-facto indentured servants. One visa worker got paid only once every 6 months. He tolerated it because complaining could get him sent back home. (It did cover his full pay, though.)

The claim H1B's are being used to "relieve labor shortages" is mostly untrue.

I disagree with a good many policies of the current administration, but they got this mostly right. I have to give them kudos.