Who would have a harder time? The company that wants to bring in employees? Sure. But I'm also sure that the top experts would be lining up to take such a job. The companies wouldn't struggle to find someone abroad.

The percentage could be reasonable, but I think it's too easily gamed. You just know the company would try and say they are bringing in entry level people for whatever they want and use whatever lowest median they could find. There needs to be a fairly significant minimum salary to avoid such monkey business.

An H1B job should be cushy. Otherwise, the company should simply raise salaries to find local workers.

This is why I say about the median salary across a branch of industry. A company is free to bring in anyone they want, but not free to pay them entry-level salary then. They should rather pay entry-level salary to local folks, e.g. recent graduates. The point is to bring above-average workers from abroad, as you say.

I don't think it's easy to game the median number, or the third quartile number if you prefer. Unless the salary distribution is severely bimodal, it should work reasonably.