...unless you look at Eastern Europe. Poland and Hungary show that homogenous nation states are not as much a thing of the past than you'd thought, and that their 'revival' (they were never dead though!) is doing just fine.
Sounds like an amazing idea /s
The populists in Poland and Hungary made a story where good aspects of the current development (for example: competitive workforce, open borders) are taken for granted and bad aspects like perpetuating big differences (like, wages, or quality of public institutions) between Hungary/Austria or Poland/Germany are attributed to some evil manipulation by the seemingly neutral EU.
Every explanation for the big wage differences is quite complicated: you can't rely on any popular simple ideology. If market is efficient, why the difference? If state-regulated society is just, why the difference? This leaves space for quite stupid populist "solutions" that are not true, but at least short.
Full disclosure: I'm from the Czech republic.
But then again, I am fairly certain that EU integration helped with our progress, especially since we had corrupt ex-commies running the show ever since '89.
It stopped them from being too greedy, plus the aid, advice and reforms did help.
And now if some people who left return out of a feeling of patriotic duty or just wanting to improve their home country, they'll be much more effective with the knowledge they gained in western Europe...
The ability to manufacture for cheap and export without too many taxes and customs headaches really helped, too, and we've set a very low corporate income tax to attract foreign (mainly EU) companies here (which worked).