Isn't this problem unrelated to cryptocurrency?

There will be the US dollar, and the people involved will be incentivized to keep its value high, e.g. by pressuring or invading other countries to prevent them from switching to other currencies. Or they'll be incentivized to adopt policies that cause consumer and government debt to become unreasonably excessive to create a large enough pool of debts denominated in that currency that they can create an inordinate amount of it without crashing its value.

Or on the other side of the coin, there will be countries with currencies they knowingly devalue, either because they can force the people in that country to accept them anyway or because devaluing their currency makes their exports more competitive and simultaneously allows them to spend the currency they printed.

If anything cryptocurrency could hypothetically be better at reducing these perverse incentives, because if good rules are chosen at the outset and get ossified into the protocol then it's harder for bad actors to corrupt something that requires broad consensus to change.