All I can do is throw my anecdotes into the pool: I mostly have met two types of Iranians: Those that fled in the 80's post-revolution, and those that come to the US for university (90's, 00's, and 10's).
All of them have been anti-regime.
I have met a few that came for other reasons (not education and not the 80's stock). Yes, those are either pro-regime or neutral.
My guess is that what rayiner says is correct: The majority of the Iranian diaspora in the US is self selecting and not representative of the full population.
My guess as well. As an Iranian outside of Iran, I see that my folk in Iran are way angrier, more disappointed, braver and determined against this injustice than I (we outside) am. It’s common sense.