Do you have any empirical evidence that H1B is an effective "weapon against high tech salaries" in the income range that Google pays?

I think that whatever is going on in the lower end of the market, there is still a substantial shortage of labor in the higher jobs that cannot be made up domestically anytime soon. Higher end jobs tend to have a much less elastic labor pool because fewer people can do the work.

Whatever the impact is for tech workers, for the general public it is definitely a bad outcome to have perpetual labor shortages at tech companies; it just means that they get their products/features/bug fixes/other improvements more slowly.