I mean, the US Dollar is a "pegged" currency under that definition too. A while ago I read an economic analysis that said the US would optimally have five regional currencies (instead of the single one that it has today) to account for internal trade and wealth imbalances.
What makes the US dollar work in practice is the active role the federal government takes to internally rebalance the economy through taxation and spending, particularly with defense spending and social programs like Social Security, Medicare, and the FDIC. People in wealthier states (including myself) like to complain that we get a bad deal because we get less back from the federal government than we pay in but that's a crucial feature of the system that keeps it from getting too unbalanced.
Additionally, in the US the federal government (for all practical purposes) is not required to maintain a balanced budget while the state governments are. This constrains the ability of state governments to issue too much debt while still providing a relief valve for emergency spending needed during economic downturns or other crisis (such as the COVID-19 pandemic).
I expect that sooner rather than later the countries that have adopted the Euro will evolve a similar system, shifting the bulk of the costs of their social programs (pensions, unemployment insurance, medical care, banking insurance, etc.) to the EU itself and giving the EU the power to tax and borrow as needed to maintain those programs. It will be a hard sell to Europe's wealthier economies, since it would be a major transfer of their wealth to Europe's poorer economies, but I suspect a future crisis will force their hands if the alternative is the dissolution of the EU (Brexit has shown everyone how badly leaving the EU can hurt).