It's very clear that a strong AI/AGI would vastly surpass all humans combined. We've already seen shades of this with Chess AIs(all humans combined still can't beat a 3000 elo chess engine e.g.), hell even Kasparov vs the world showed showed us that the rest of the world combined can't even match a single high end human.

>I think going forward we're going to need much more clarity about what "superintelligence" really means.

This was already well defined by Bostrom in 1997: "An intellect that is much smarter than the best human brains in practically every field, including scientific creativity, general wisdom and social skills"

>Currently it seems like AI is essentially mimicking collective human intelligence, which means it is probably constrained at that level, as that level is the source.

There are no indications at all that it is constrained to that level.