As a non American who would benefit from a H1B visa, I'll say the "America first" people are right when it comes to the H1B visa misuse.

Currently it is used as a tool to extract maximum labour for cheap compared to hiring Americans. We don't call it slave labour because the immigrant is paid decently, but they are held hostage by multiple factors; career aspirations, family expectations and the like.. So easier to manipulate while denying opportunity for actual Americans.

Needs serious reform. A simple one is, pay H1Bs higher salaries than market rate. This would create the economic incentives for companies to use H1Bs only when really needed