I cannot answer your question, but I do not notice much difference. Just got back from the Southern Hemisphere (their winter) flights jammed, no "u"s - no room anywhere.

HI flew back from CDG Sun, he said that everything in all classes was sold from noon onwards (according to staff) - I have no idea whether the yield from all these tickets was worth having or if they were transfers at LHR/LGW, but everything was packed - including his LCY.