You're right. Unfortunately USYD doesn't show what the cut-offs for unis were in previous semesters however, so the only way you'd get the info you're looking for is by asking people who went on exchange to whichever uni you're interested in what their WAM was at their time of application (which will be quite an awkward conversation unless they're your friend lol).
There is a second way to get a general idea though, and that's by seeing what the WAMs were for UNSW. If you followed my earlier suggestion, you'd get to
this thread, which has
this pdf posted by HeyJes. University partner list differs of course, and demand at UNSW can be different to demand at USYD because of the general difference between USYD and UNSW culture (UNSW more tech-y, USYD more Arts-y) and other reasons, but if you just want get an idea of the WAM cut-offs it should serve well.