These things don't get mentioned much around brexit and I admit I don't know much about them and could be getting this all wrong but the way I see it is. It all started as just a free trade agreement and was a good thing for all when it got beyond that it never seemed try try and tackle the issues of why people move from east to west to get more money. I so should have been a force to deal with the migrant crisis but totally failed. The euro was never a good idea and just caused a big boom followed by a big bust for many. I could have dealt with Amazon, starbucks etc avoiding corperation tax. Instead it seems to be about putting red tape everywhere which bid multinationals can deal with but there smaller competition can't.
The EU has never really just being about trade, right back to when it was first established as the European Steel and Coal, one of the reasons given for it by Robert Schumann (French Foreign Minister) was to ”make war not only unthinkable but materially impossible", with the community estabilishing a common market for coal and steel helping to neutralise competition between its member states over resources.
Today the concept of a war between European powers is pretty much unimaginable but in the fifties it was only a few years after the horrors of the Second World War, (with two major European conflicts being within living memory of much of the population). The point is the EU and it’s predecessor have never being just about free trade.
In defence of the Euro arguably Greece and potentially Italy should not have being allowed to join. But one big advantage is it removes exchange rate volatility within the block.
Amazon and Starbucks would find a ways to avoid tax regardless, tax havens have pretty much existed as long as tax has, you don’t think all those companies are incorporated in the Cayman Islands for the weather do you.
As for red tape the EU has arguably reduced not increased red tape, you are always going to need some degree of regulation and better to have one set to deal with across multiple counties than have to deal with 20+ different regulatory systems. Here is how you currently export to mainland Europe, find customer to buy product, pack product, dispatch via courier of your choice.