> The biggest issue is giving up one of the biggest instrument of control over the economy to a supra-national non-democratic organisation

This is the point. Germany managed to set up a really independent central bank (which is a non- democratic, bureaucratic, etc… thingy) and inflation was at the target for decades. Italy, France, etc… didn’t, and inflation was 2-3 point above target and above the German levels. So they joined the Euro, which has a governance very similar to the Deutsche Mark.

To this day, inflation in European countries outside the Eurozone is higher.