A cash infusion is the worst possible move if you want to de-fang Iran. Not only is the US giving them 300 billion but also lifting the sanctions and possibly allowing them to charge a toll on the strait, which is another source of cash flow. Iran has a large population, a highly educated population and some of the largest oil reserves in the world. The US has caused friction with its allies, shown it cannot/is not willing to protect the region, lost billions of dollars, and tanked its and the world's economy all for Iran to have very ephemeral setbacks and to be given the keys to mind-blowing wealth. Wealth that can be used to do all the things that made them a threat but on an even grander scale.