There are many kinds of people on H1Bs. There are people that are brought here by the consultancies you mention and there are graduates from American Universities who get H1Bs after or during their OPT. While I've heard that H1Bs are brought over to depress wages, although there is no data to back that up. In both these cases, there are a mixture of really good people, really bad people who got lucky and everything in between. I also know that there are rampant scams that involve faking Resumes to fake universities, however, there are many many many good people still holding out in the hope that this backlog for Indian's and some other countries resolves and lets them lead a better life.
However, according to this article[1], the number of open positions in Programming and Comp Sci. was about 500k and the US produced about 50-60k grads a year, 85k H1Bs wouldn't be enough to take all the jobs and flood the job market.
Also, from my own experience, I make over $250k as a Software Engineer, stuck on an H1B forever, while people who were born in other countries get to move on to a Green Card, even if they earn less than that. My company interviews hundreds of people, settling for 'good enough' and yet struggles to fill many open positions.
[1] https://qz.com/929275/you-probably-should-have-majored-in-co...