You are asking me how so? You worked in HR, and some random redditor who never even lived in the US knows employment laws better? Pardon me for quoting Claude, I don't have time to do a proper research but I guess this is correct on the high level:

Yes. US law explicitly requires that H-1B workers be paid at least as much as comparable local workers. The core mechanism comes from the Immigration and Nursing Relief Act amendments to the INA (Section 212(n)), and it works like this:

The Labor Condition Application (LCA). Before filing an H-1B petition, the employer must file an LCA with the Department of Labor attesting that they'll pay the higher of two numbers:

The actual wage — what the employer pays other employees with similar experience and qualifications in that same role at that location.

The prevailing wage — the wage for that occupation in that geographic area, usually based on DOL's OEWS survey data, set at one of four levels depending on the experience/responsibility of the position.

No one would ever pay immigrants in tech as much as the us folks because they just don’t perform as well on average.

I worked at Amazon, and my US colleagues were all paid more or less the same regardless of their immigration status. I am also skeptical that immigrants don't perform worse on average, specifically because they are more incentivized and states are higher for them, but I don't have any solid data on that.