Wouldn't the difference have to be substantial to justify the hiring from abroad, integration into the company and so on?
The difference is quite substantial, I can assure you.
In the long run, US, European and Asian companies save BILLIONS by outsourcing.
Are laws supposed to protect American workers from competition from abroad
Remember just one thing: National and international laws are supposed to protect the Elite and the Elite only, NOT the average worker or Joe Six Pack.
but not supposed to protect US employers from paying too much for workforce?
There is no such thing as "paying too much" for workforce. And paying "too much" according to what criteria, exactly?