The problem is that, in the example quoted, no one had that control. Gold mines run dry and you're fucked. Not because some incompetent banker is controlling the gold supply, but because there is no more damn gold. The most competent financial advisor of Rome -- a figure so gargantuan in the field of finance that, if transplanted to the modern world, would not only win that fake Nobel prize for economics, but would cause every other economist to retire out of shame -- would have been powerless. Because there was literally no more gold.
Obviously, it wasn't the end of all things -- new mining facilities would be open, sometimes processes would be optimized in older ones, wars would be waged, but these things took time and needed money.
I'm not suggesting the Romans needed to venture westward and discover the Americas, but did they really have no other options?
Apart from that, there was also normal economic and population growth – even without trade, if your population and economy grows, you'll need more money if you want to keep prices and wages stable.
So, they had several options:
• Conquer places that have gold! That went well for a few centuries, until it didn't any more.
• Debase the currency to make more of the money still here. That was, unsurprisingly, massively unpopular. And because monetary value was still tied to precious metals, people just started to hoard old money to melt it in later (something you still occasionally see with e.g. copper pennies), which led to all sorts of economic problems (occasionally crashing all the way down to barter trade).
It's just that having this debate is pure luxury already. Otherwise it'd be "where the hell do we get the gold we need to fuel our economy?" or "what do we do with all the surplus gold that's ruining our economy?".
> but alternatives such as Bitcoin become increasingly interesting in countries plagued by hyperinflation.
Bitcoin, really? Private currencies where inflation is at the mercy of random developers who may or may not control significant currency reserves as well?
Using foreign currencies to supplant or replace a failed domestic currency isn't a new phenomenon, nor limited to "crypto""currencies" (the Balkans used the German Mark extensively in the late 90s, and US Dollars get you far in a lot of places).