The dollar is only one currency. SWIFT is the network that allows transactions in multiple currencies across banks easily. There are a huge number of sovereign currencies in the world that you can buy things with, not just one. Probably more central banks than there are large mining pools.
If mining pools conspired to, say, fork a chain because somebody stole a lot of tokens due to a bug, it amounts to the same kind of control.
Miners are distributed and there is the well known problem of 51% of the mining pool being controlled by a single party, but they would have to control 100% of the mining pool to be the equivalent of the Fed.