

A universal global currency isn’t a bad idea, necessarily, but putting all that power in the US’s hands was always bad. Any time anyone tried to do anything the US didn’t like they’d get slammed with structural readjustment and sanctions and blockades and regime change. It was always a tool of underdevelopment and imperialism.
Ask Cuba how great it was that the dollar was the reserve currency.
In a multipolar world there is no one country that gets to be in charge.