The greatest and most annoying retcon I see is the Alliance. It used to be a group of self-serving racist, xenophobic and quite maniacal groups of people. The old guard changed (even though the Night Elves and Worgen are somehow supposed to have changed too, no one knows how), and now we have the flawless group of morally superior people who cannot do any wrong. It is also enforced by many Alliance players, who now see it as cannon and would be outraged if anything changed for the worse.
The end result?
Whenever we have conflict, it must be the Horde starting it, the Horde being cruel, genocidal, out of their minds, and the Horde paying the price. Looking at the US forums, there are people who’d want Horde paying even more price for recent events. We’re almost out of old guard characters, Forsaken and Orcs are almost without identity, Tauren became some side-dish peppered with Anduin and Jaina taste. What did Alliance lose in terms of leaders? Varian, who came back after a few expansions missing and we cannot even guarantee he won’t return after Shadowlands?
The Horde is being systematically destroyed just for the sake of continuing the story “in an interesting way”, provided that the Alliance community would not have their angelic robes tainted. This retcon is destroying an entire community and years of fun and experiences…
If you see many horde simply not caring about Teldrassil or defending Sylvanas, hating Calia or any other means of “redemption”, think about it. From a lore perspective you are right, but outside of it, we are just gamers constantly f-ed up by the devs and being bled dry.