The only time the EU (or EEC as it then was) has delivered impressive growth was the 1950 to 1970 period, known as the period of "catching up".
The European elite thought the A8 and A10 would similarly "catch up". But in 1950 to 1970 there was no single market which by definition destroys many Member States' industries. There was only a Customs Union.
After 1970 worker productivity in the EEC still grew quite rapidly but this was offset by restrictions on hours of work.
In general it is thought that that the existence of the EEC/EU has made growth 0.5%pa higher than it would have been otherwise.
Big deal! And it's at the cost of its interconnected and insolvent banking sector, its vast taxes on energy, the power of the Commission Bureaucrats to demand that Member States shut down parts of their economies, high youth unemployment, common foreign policy, the straitjacket of EMU, the distortions of the CAP, VAT, the list goes on.
Imagine an independent Bulgaria in its traditional role of electricity exporter to the Balkan region, able through its bilateral agreements to profit from its proximity to Russia, Turkey, the 'stans and its traditional friends in the Far East. And a discriminatory 80 leva tax on every non-Bulgarian truck hurtling towards "Europe". Brits not allowed to live there unless they can pass simple tests, pass a means assessment and undertake not to keep dogs. Doesn't sound too bad to me
But as I say they have a genius for doing the wrong thing. I think they will face the consequences soon. Full speed ahead back to 1943.