Re: So, to sum up. . .
"Most of the world are not members of the EU."
Most of the world haven't been UK business's home market or a major part of UK industry's supply chain for four decades. They still won't be so there's no difference there.
The EU has been UK business's home market and a major part of UK industry's supply chain for four decades. Now it won't be. That's where the big difference lies and it's not a good difference.