It is impossible to integrate manufacturing, finance and service economies and to maintain solidarity at the same time.
I disagree...it's necessary to maintain solidarity. After all I'm much more inclined to support people close to me than outsiders...Germans being solidary with Greeks was pushing it, especially as it became known that for example greek pensioners got earlier more support than german pensioners, so it was hard to explain to german poor pensioners why they should pay so that the greek pensioners could live on better than them.
But if the social systems for example would be all integrated then all pensioners had the same rights and duties, no matter if they live in Greece or Germany and it would be much easier to feel solidary towards each other.
Making Italians accept German economic values is impossible unless you turn them into southern Germans
There is no economically "good" country nor an economically "bad" country.
Every country has it's economically well off, successful regions and it's poor, less developed regions. That has nothing to do with the EU. But they get now support funds from the EU with the chance to invest in these regions, to develop them.
But without any closer integration nobody from the outside...say...from Brussels... can influence how the national gov is using these support funds, so it happens that poor regions stay poor, but that is not the fault of the EU and those support funds.
To make better choices to help with the development of poorer regions it would need a common economical ministry/department...but that would mean again much closer integrated economies!
The only thing that would happen outside the EU is that they either would have to chuck out this support by themselves now again or cut it out. That's the only options! These regions won't become developed now just because the country decided to leave the EU...there is no sense in that!