Well, the saga continued the next day, when the same thing happened AGAIN! Showed up at check-in for PVG-ICN to be told that today's plane was a 2-class configuration. Oh no! Well, overall the situation was handled much better, though, and I consider it resolved.

An apologetic local Asiana manager told me about the situation, immediately offered the downgrade confirmation without me asking for it and let me know that there was nothing he could do in Shanghai but Asiana would of course properly compensate me and that I should take it up with staff in Incheon. He handed me a pass to the first-class lounge (which I did not have access to the previous day :-( ) and escorted me to security.

Staff at Incheon initially gave me a similar line to Air China that I should contact US Airways, they also tried to tell me that since this was an award ticket that no compensation was due. I did not let them off the hook, but politely and firmly insisted that this was solely OZ's responsibility and US had nothing to do with it. They've been mostly professional in dealing with this incident so I wasn't looking to wrangle much from them. I was simply looking for a token of remorse beyond "we are really sorry", considering I got the F lounge, the agent did not blink even though I checked in 10 kg over the baggage allowance and the flight was too short to make much of a difference between F and C.

Asiana did offer that token in the form of 150$ cash when I boarded the flight to Incheon and even though I feel it's a bit of a shame that I had to insist more than I think I should have (given it was solely and squarely their responsibility), I consider the Asiana issue resolved. Just out of curiousity, did I let them off the hook too easily?