One problem with a very high minimum salary is that due to the disparity in cost of living, only companies that could afford H1B workers would be from a few cities like SF and NYC. As a side effect, it would increase the diversity of those cities and not anywhere else. I don't think it is ideal - it concentrates immigrants into a small location; and does not allow immigrants to live in a place of their choice.
I think you are mixing up cause and effect - it's not easier from a financial standpoint for companies in NY to pay high salaries, it just happens that companies who can afford high salaries are located there because it's easier to get top talent at those locations.
