Returning to the original post, I think a lot depends on the crew and legacy vs non.
Had a really bad flight in CW upper deck to SFO in November with the attitude of the two stewardesses being ‘can’t be bothered’ especially when I had a problem with the IFE – rolling their eyes, dismissing my queries etc. When I flew to LAX a week later, the CSD came and did their usual GC holder post-take off chat and I mentioned it. She asked if I had complained afterwards and I said no and she insisted that I do so.
By comparison the LAX flight on the A380 was superb and exactly what you’d expect. I did write to the BAEC and got 12k Avios as compensation, but I’d rather have had a smooth and trouble-free flight and not have had to complain in the first place.