Guys I just want to update you on the results and I hope this could serve as a reference for future international transfer students who want to transfer from an Australian uni to a U.S. one.
Basically it somehow worked out. I was dinged by Wharton and a few other ivy schools but managed to get into Columbia. I seriously doubt that the U.S. admission officers have no idea about what the f*ck a high distinction is and I guess they might have treated a distinction as B or something. If you want to transfer, make sure that you explain the grade conversion in detail. For UNSW students there is a conversion graph which basically says HD=A+ and D=A or something.
Again the process is REALLY TOUGH that I slept like only 2-3 hours per day in the application season. Also, Australian unis do not have much experience handling international transfers so you should expect:
1. "Wat!? Why leave our school?!" from departmental head whom you must ask to write you a report. It would somehow work out but do not expect it to work out smoothly, NO WAY.
2. No response from professors from whom you are supposed to ask for a recommendation letter. (seriously I got one prof with whose classes I got two 90+ hd and participated actively in lectures and he did not even bother to reply to my email lol)
3. If you are on an exchange, the exchange managers might become rather picky on what you did and you might be asked to terminate it. I suffered from this so basically I only stayed there for 1 sem.
Although it worked out and I got into an ivy, I have to say that the support I received from UNSW was minimal, if not none. If you want to do an international transfer, be prepared to be treated in the same way and I would not be surprised if they try to make it harder for you to transfer.
Overall I think these annoying actions taken by UNSW administrative and academic departments really pissed me off that I became much more determined to transfer out. It is hard to believe that my Wharton professors, who only taught me, an exchange student, for 1 semester, were much more supportive than my UNSW professor with whom I exceled in two 3XXX courses as a first year student. Also the administrators' attitudes made me feel that literally NO ONE cared about me; this would never happen in an elite US college where every single student gets some attention from advisors.
An additional update, I think the ATAR 99.5 myth for ivy is a bit misleading. I sort of screwed up in the final exams and only got a 98.3 in ATAR but I do not think the admission officers in ivy leagues really have a clear idea of that.
Good luck to all the future transfer applicants!