The reserve currency isn't where power lies.
It's convenient (at most) for people in the USA to have the dollar as the de facto reserve currency. It's also convenient for people outside the US to have a dominant reserve currency -- having a small number larger than 1 would be OK, but not especially convenient and in the end would still converge back to the largest one, which would be the incumbent.
The convenience for the US is simply that if you do any foreign transactions you can easily see their value. Also, domestically, if you borrow you have a lot of predictability in interest rates. That's basically it.
If you are, say, Australian and use aussie dollars the same is basically true! If you're a very small country, or your economy is a basket case and there is no real lending in your currency then the reserve currency doesn't help you much -- you have to borrow in some foreign currency so currency fluctuations hurt can hurt (or help) you, and you have no control over it.
The USD is a good choice because foreign exchange is a small part of the size of the total amount of money, and the amount doesn't fluctuate a lot. It might feel like it does when you live in the states, but really it's like swimming in the ocean: there's some surface chop, but the big waves have such long wavelength you don't even notice them.
The real power is in control of the banking forex interchanges -- you can see them being used against Russia and Norks, for example. In reality the US doesn't really have a lot of control over them except by persuading other important economies to go along. It's like a very weak form of nuclear weapons: their value comes from not using them. And for forex -- well let's just say the US control over that is negligible, specifically because it's the reserve currency. So not much of a weapon at all.
It's pretty easy to not use the dollar as an exchange currency -- think of hawala, with perhaps, say, its own private set of AED/PKR exchange rates (notice the plural!). Or china and iran selling oil without the dollar. These work for small sums, but at the end of the day people work out the exchange rates...by comparing vs dollars, the same way a translation between Maltese and Estonian probably goes through English or French. This is why having more than one will regress back to the incumbent barring a major, and very slow (decades/centuries scale), problem.