Ok, that is different though... you are arguing the US CHANGED their policy, and you don't like the way they changed it.
That is different than saying they were not in control of their monetary policy... they have always been in control, you just liked the old monetary policy better
Have they always been in control? Yes, for the entire existence of the US it has been legally capable of creating a US Dollar and of turning it into a fiat currency.
However, for large swaths of the time the US has been around that has not been politically feasible, and I'm not sure it would have been economically feasible, fiat currencies seem to have taken a while to gain stability and acceptance.
For a large period of time the US was on a gold standard and de facto did not have control over monetary policy. It doesn't matter much that they technically had power if they didn't use it.
That is different than saying they were not in control of their monetary policy... they have always been in control, you just liked the old monetary policy better