Not related to the comment, but in general I agree with you.

You can't have a single monetary system without complete unification, including tax systems, budgeting systems, governance models, retirement systems, benefits. I mean, you can, like we have now, but it's not sustainable, and eventually we all have it worse.

As a European, I would not want to go that way, since I'm afraid such a unified EU will be a bureaucratic monster that is even more centralized than the USA, and way more autocratic than any current EU state.

I'd rather take a step back, dissolve much of the EU's competences, and go back to pure trade union, dissolve the EURO as a currency, and let every member state take sovereign decisions on their own.

Even more centralized than the USA? That must be an outsider's view. You are aware that each state has its own tax laws? Corporate laws? Even criminal laws and traffic laws? And so on? Obviously there is federal law, too, but that's more of an umbrella covering all states in addition to local laws. The USA is a federation, just like Germany, Switzerland, or Austria are federations, and one common complaint you get out of these nations all the time is that they are not centralized enough!

The EU, on the other hand, is not a federation, it is a association of nations trying to figure out how to go together, be it as a federation or something different, because in today's world you need size and power to survive. Any EU state alone would be insignificant on the world stage and being sidelined one way or the other. The most powerful inside the EU would suffer the most, e.g. Germany or France, because while the EU is second or third on many metrics, the individual nations are small. Depending on which ranking you look at, the EU is just behind the USA in military and economic power, sometimes it is behind China in economy, too.

The strongest individual economic power of the EU is Germany, which globally usually comes in 4th place after the USA, China, and the EU as a whole. But this is deceiving, when you look at the absolute numbers. Germany's output is impressive for its size, but is still only about a quarter of China's! Germany alone is a dwarf and without the EU would be inconsequential. The post-Brexit UK is just learning this the hard way and all the sovereignity does not matter a damn. The top leadership of EU nations are not stupid, even if they could explain their reasoning better, and thus try to keep the EU going, despite its many flaws.

This is a Chesterton's Fence situation.

I recently became much more pro-total-unification, so let me give you this counterpoint: individually, European nations are no match to the major superpowers, neither economically nor militarily. We'll get gutted by divide-and-conquer approach. In contrast, bound much closer together (particularly with some form of pan-european armed forces), the EU would become a proper global superpower and a counterbalance for the USA and China.

There is not a single example of a multiethnic or culturally diverse empire or state that was successful after the rise of nation-states at the end of the 19th century.

All of them crumbled either peacefully or in bloody wars.

Why do you think such a bureaucratic monster that no one really wants would be an exception?

Maybe we can try it again in the 24th century, when the humans evolve enough, but for now, your best bet for a successful country is either an ethnonational or religion-national state.

You cant really believe any of the EU countries actually want to work together? The EU was only possible with the premise of countries keeping their autonomy. Believe me when I say that us Germans would rather go to war than merge with France, just as an example.