I think it shows excessive certainty in a counterfactual to say that Iran "would have never wavered" without Trump pulling the US of the deal first, but if it had wavered then it certainly wouldn't have had nearly as many ready-made talking points for why it was doing so.
It's absolutely certain that Iran wouldn't have wavered this soon without Trump's decision to pull out. The Iran deal was far from perfect, but the idea that returning to sanctions would cause Iran to change course in a desirable way was utterly idiotic.
