Europe’s biggest problem, I think, is its lost mojo. There’s plenty of good ingredients, plenty of challenges too. It can still go either way. Hell, at this rate it might outperform simply because US and China blow up due to domestic problems.
The thing about mojo is that it’s super hard to predict. It might stay where it is and Europe’s share of global GDP might decline to nothing. Or it might rekindle out of nowhere due to some impulse.
Either way, middle democracies are a somewhat threatened species now, and from their individual PoV an imperfect union might be much better than efficiently staying on their own.