The Fed matters because it can control the supply of the worlds reserve currency, full stop. It has several tools, not just interest rates but: bond purchases, repos, etc.
The Fed is the village by the river. It can take water out of the river or put it in, but it doesn’t control downstream use of the river. It’s goal would seem to be a stable flow, though it doesn’t always accomplish that. Whether it is reactive, or proscriptive it is very powerful in its actions.
One could make the argument that without the Fed Congress couldn’t function. People love services, but hate taxes.
