I mean just that abstraction is central to human intelligence and general intelligence in a way that seems necessary (integral and inseparable) and part of the very definition of general intelligence, whereas WM is not. I can imagine something a lot like me that wouldn't use WM, but I can't imagine anything remotely like me or any other kind of general intelligence that doesn't have something very much like our ability to abstract. But I think that's pretty much what I've said already, so I'm probably not helping and should give up.