But as usual your linked blog post (very self-referential) is off topic.

The ECB is a part of the european government; but hardly the only one. There is the commission, the parliament, the council, the court. The ECB is not even the most powerful part: The council is equal in power, the court more powerful.

So if the EU is sovereign and I think it is, the ECB is one aspect of it. Not more or less.