The "sovereignty" argument is a bit misleading though. It's basically regulatory alignment.
I think it's a real argument personnally and the heart of the issue. That was the main question of the Brexit referundum: do you want to be a part of this pan-European union of people and surrender some of your country power to this union?
You can argue that the subsequent trade agreement and the alignment that followed have reintroduced some of the same constraints, which is true, but practically and conceptually speaking it is a very different kind of situation.