I am well aware of the required sponsorship, but I've seen this first hand and it appears pretty easy to get one as long as they don't have poor English skills. Many companies hire in large numbers ("incoming classes") and whether you are an international or not has 0 bearing. With the increasing number of international students each year, it seems that competition in the job market will only get worse especially since everyone is aiming for the same desirable roles at desirable companies.
I'm pretty sure it definitely matters from a legal standpoint for a business whether or not the person they're hiring is a citizen of their country. You might be saying that so many students on visa eventually get citizenship if they graduate and wait long enough, which might be true, but then they aren't really international students anymore.
With a growing class of educated individuals, if the the rate at which those individuals are able to capitalize on ideas remains constant then the rate of job creation as a percent of the total population should remain constant.
The real problem is that hiring US citizens is simply to expensive for most industries causing the use of extralegal means and or loopholes in existing laws to hire outside individuals at significantly reduce compensation.
Big assumption. Even with Master's graduates, you're going to look at a lot of technicians and others that have minimal idea input. The people capitalizing on ideas are the ones hiring educated labor, and since capital is not finite, there are only so many people they can hire. This is why it's a joke to think a more educated workforce is automatically a more productive one. A person can graduate with a M.S. in biochemistry, handle a pipette, do some chromatography, etcetc, but those are still just merely manual skills if they're just taking orders. Get enough people doing it and it's literally no more valuable than operating a lawn mower or pool skimmer.