I agree that when you look at the total number of H-1Bs being awarded vs the size of the total labor market in sofware engineering, it seems unlikely it is having a massive effect.

And if you look at the massive absusers of the system(Toptal, Wipro etc), that use it to lower pay, I feel as though many of those jobs would have instead been outsourced oversees anyway. So at the very least, for a US perspective, the taxes and consumer spending are still partly captured in the US as opposed to another country.