I can't speak for the earlier commenter, but I think there is a large gap between what the EU does today and what it would need to do to be a "superpower". It is left to our imaginations to guess at such a future, and so disagreements may just stem from different imagined scenarios.

I don't think the US would be a superpower if the treaties, tariffs, and military control were parceled out to the individual states and each state governor and state assembly decided when to work as a block and when to act independently.