The "immense power" mostly boils down to cheap imported consumer goods and unemployment/underemployment. You actually have to actively fend off the negative effects or it will drag your country down because of right wing populism.

The misconception is that economies are static and always in a certain specific state some boomer grew up in. e.g. supply side stimulus will fix all problems because all problems are supply side problems (just think of the shortages after WW2). Of course, reality is not that simple.

What if the supply side has been saturated and you are in a liquidity trap and you have demand side problems? A "world reserve currency" can only make things worse because your government is forced to take on an increasing amount of debt and it has no power to stop the process beyond getting rid of your "world reserve currency".

The only good news is that some presidents want to use the debt on infrastructure investments. It's the textbook way to get out of a liquidity trap. Turns out this has never happened and instead we get trump tax cuts for the rich. Immense power my ass.