I have come to agree with this. I was a supporter of the Euro and Emu since the 1990s, but I think I've been convinced that trying have a single currency without full fiscal union is folly.
You should choose to either have balkanised currencies, or a federal financial bucket, meaning the richer countries subsidise the poorer ones.
We went with Option C in Europe, and I don't have a lot of confidence that the Euro can survive in the long run in the current system.
Each separate state in the US has a fixed exchange rate with each other (1 USD = 1 USD), but our fiscal policy is administered by a central authority that adjusts for overall US conditions, not just individual states.
The answer to the Zim problem is not the adoption of multiple currencies they don't control, though, unless they are just completely abandoning the goal of self governance altogether.
That may be exactly what they're doing. Mugabe can't live forever, and his cronies could well be selling the country off to China, with an exit strategy in place to spend the rest of their lives in comfort in a third country.
Zimbabwe became a dystopian cliché of hyperinflation and societal breakdown, with 80% unemployment and 100% inflation per day. It is the current example we use when we summon up the absurdist "wheelbarrows of currency" imagery. Basically, they were limited to a barter economy, with a thick layer of authoritarian interference in what became a very limited system of production and distribution of goods & services.
To create a currency union that's sustainable, you have to commit to a fiscal union (where there is stable net wealth transfer from New York to Nebraska through things like social security), and/or to a very stiff amount of labor mobility & remittances (where internal migration to the site of available employment is as common as in the Dust Bowl). The EU did not have enough of the latter (for a bunch of reasons), and chickened out on the former; In that case failure was unavoidable, and credit availability simply delayed an inevitability.
You can give up 'monetary sovereignty' in a long-term stable manner and sustain a functioning economy if you're willing to do these things. The United States did. We have whole regions that would be depopulated without social security, Medicare, and welfare to keep the population alive without its manufacturing base. We have abundant internal migration.
But Zimbabwe is a whole other sort of thing. They didn't relinquish much of anything when they gave up their currency; They had to build a new economy from the foundations on up.