If it doesn't count for prevailing wage, does it count for the evaluation of the compensation distribution in the first place (genuine question, I'd assume no for consistency of measurement but yes if e.g. W2-reported compensation is used as reference)?

You can doubt it all you want. I was also not claiming that fangs pay 95th percentile wages. I said that in my experience they pay h1bs pretty well (not that different from domestic entry level engineers).