Paying prevailing wage doesn’t necessarily mean that’s the salary a company would have paid/are paying to American workers in the same role. Three-fifths of h-1b jobs are certified at the two lowest prevailing wage levels and the median age of an h-1b beneficiary is 33 years old.

DOL does have the data to determine prevailing wages. In fact the wages reported in the application for H1B is often lower than what the immigrant is getting paid because DOL does not accept bonuses and RSUs and other options as guaranTeed wage. So you could have an H1B petition with $200k but in reality they could be earning $300k+ with bonuses and RSUs.