I’ve rarely seen them used for that purpose, but of course that’s my personal observation and I have no data about it. A lot of H1B folks I worked with were solid backend/mobile devs. I enjoyed working with most of them but it’d be a stretch to say they were uniquely qualified. I do notice they feel a lot of pressure to never push back on anything due to how they set up the H1B system. Not always the case but often. I always felt that they were being exploited in that way.